Does the Russia-Ukraine conflict pose a possible nuclear war? Is Russian move to annex four Ukrainian regions a nuclear war triger?

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Armed conflict in eastern Ukraine erupted in early 2014 following Russia’s annexation of Crimea. The previous year, protests in Ukraine’s capital, Kyiv, against Ukrainian President Viktor Yanukovych’s decision to reject a deal for greater economic integration with the European Union (EU) were met with a violent crackdown by state security forces. The protests widened, escalating the conflict, and President Yanukovych fled the country in February 2014.

One month later, in March 2014, Russian troops took control of the Ukrainian region of Crimea. Russian President Vladimir Putin cited the need to protect the rights of Russian citizens and Russian speakers in Crimea and southeast Ukraine. Russia then formally annexed the peninsula after Crimeans voted to join the Russian Federation in a disputed local referendum. The crisis heightened ethnic divisions, and two months later, pro-Russian separatists in the eastern Ukrainian regions of Donetsk and Luhansk held their own independence referendums.

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Armed conflict in the regions quickly broke out between Russian-backed forces and the Ukrainian military. Russia denied military involvement, but both Ukraine and the North Atlantic Treaty Organization (NATO) reported the buildup of Russian troops and military equipment near Donetsk and Russian cross-border shelling immediately following Crimea’s annexation. The conflict transitioned to an active stalemate, with regular shelling and skirmishes occurring along frontlines separating Russian- and Ukrainian-controlled eastern border regions.

Beginning in February 2015, France, Germany, Russia, and Ukraine attempted to kickstart negotiations to bring an end to the violence through the Minsk Accords. The agreement framework included provisions for a ceasefire, withdrawal of heavy weaponry, and full Ukrainian government control throughout the conflict zone. Efforts to reach a diplomatic settlement and satisfactory resolution, however, were largely unsuccessful.

In April 2016, NATO announced the deployment of four battalions to Eastern Europe, rotating troops through Estonia, Latvia, Lithuania, and Poland to deter possible future Russian aggression elsewhere on the continent, particularly in the Baltics. In September 2017, the United States also deployed two U.S. Army tank brigades to Poland to further bolster NATO’s presence in the region.

In January 2018, the United States imposed new sanctions on twenty-one individuals–including a number of Russian officials–and nine companies linked to the conflict in eastern Ukraine. In March 2018, the U.S. Department of State approved the sale of anti-tank weapons to Ukraine, the first sale of lethal weaponry since the conflict began. In October 2018, Ukraine joined the United States and seven other NATO countries in a series of large-scale air exercises in western Ukraine. The exercises came after Russia held its own annual military exercises in September 2018, the largest since the fall of the Soviet Union.

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In October 2021, months of intelligence gathering and observations of Russian troop movements, force build-up, and military contingency financing culminated in a White House briefing with U.S. intelligence, military, and diplomatic leaders on a near-certain mass-scale Russian invasion of Ukraine. The only remaining questions were when the attack would take place and whether the United States would be able to convince allies to act preemptively. Both were answered on February 24, 2022, when Russian forces invaded a largely unprepared Ukraine after Russian President Vladimir Putin authorized a “special military operation” against the country. In his statement, Putin claimed that the goal of the operation was to demilitarize and denazify Ukraine and end the alleged genocide of Russians in Ukrainian territory.

In the days and weeks leading up to the invasion, the Joe Biden administration made the unconventional decision to reduce information-sharing constraints and allow for the broader dissemination of intelligence and findings, both with allies—including Ukraine—and publicly. The goal of this strategy was to bolster allied defenses and dissuade Russia from taking aggressive action. Commercial satellite imagery, social media posts, and published intelligence from November and December 2021 showed armor, missiles, and other heavy weaponry moving toward Ukraine with no official explanation from the Kremlin. By the end of 2021, more than one hundred thousand Russian troops were in place near the Russia-Ukraine border, with U.S. intelligence officials warning of a Russian invasion in early 2022. In mid-December 2021, Russia’s foreign ministry called on the United States and NATO to cease military activity in Eastern Europe and Central Asia, commit to no further NATO expansion toward Russia, and prevent Ukraine from joining NATO in the future. The United States and other NATO allies rejected these demands and threatened to impose severe economic sanctions if Russia took aggressive action against Ukraine.

In early February 2022, satellite imagery showed the largest deployment of Russian troops to its border with Belarus since the end of the Cold War. Negotiations between the United States, Russia, and European powers—including France and Germany—failed to bring about a resolution. In late February 2022, the United States warned that Russia intended to invade Ukraine, citing Russia’s growing military presence at the Russia-Ukraine border. President Putin then ordered troops to Luhansk and Donetsk, claiming the troops served a “peacekeeping” function. The United States responded by imposing sanctions on the regions and the Nord Stream 2 gas pipeline a few days later. Nevertheless, just prior to the invasion, U.S. and Ukrainian leaders remained at odds regarding the nature and likelihood of an armed Russian threat, with Ukrainian officials playing down the possibility of an incursion and delaying the mobilization of their troops and reserve forces.

On February 24, 2022, during a last-ditch UN Security Council effort to dissuade Russia from attacking Ukraine, Putin announced the beginning of a full-scale land, sea, and air invasion of Ukraine targeting Ukrainian military assets and cities across the country. U.S. President Joe Biden declared the attack “unprovoked and unjustified” and issued severe sanctions against top Kremlin officials, including Putin and Russian Foreign Minister Sergey Lavrov; four of Russia’s largest banks; and the Russian oil and gas industry in coordination with European allies. On March 2, 141 of 193 UN member states voted to condemn Russia’s invasion in an emergency UN General Assembly session, demanding that Russia immediately withdraw from Ukraine.

Since the 2014 annexation of Crimea, Ukraine has also increasingly been the target of thousands of cyberattacks. In December 2015, more than 225,000 people lost power across Ukraine in an attack on electricity generation firms, and, in December 2016, parts of Kyiv experienced another power blackout following a similar attack targeting a Ukrainian utility company. In June 2017, government and business computer systems in Ukraine were hit by the NotPetya cyberattack, which has been attributed to Russia; the attack spread to computer systems worldwide and caused billions of dollars in damages. In February 2022, Ukrainian government websites, including the defense and interior ministries, banking sites, and other affiliated organizations were targeted by distributed denial-of-service attacks alongside the Russian invasion.

 Recent Developments 

As the initial Russian invasion slowed, long-range missile strikes caused significant damage to Ukrainian military assets, urban residential areas, and communication and transportation infrastructure. Hospitals and residential complexes also sustained shelling and bombing attacks. In late March 2022, Russia announced that it would “reduce military activity” near Kyiv and Chernihiv. By April 6, Russia had withdrawn all troops from Ukraine’s capital region. In the aftermath of the Russian withdrawal from Kyiv’s surrounding areas, Ukrainian civilians described apparent war crimes committed by Russian forces, including accounts of summary executionstorture, and rape.

On April 18, Russia launched a new major offensive in eastern Ukraine following its failed attempt to seize the capital. By May, Russian forces took control of Mariupol, a major and highly strategic southeastern port city that had been under siege since late February. Drone footage published by Ukraine’s far-right Azov Battalion revealed the brutality of the Russian offensive, which had reduced the city to rubble and caused a massive humanitarian crisis. Indiscriminate and targeted attacks against civilians in the city, including an air strike on a theater and the bombing of a maternity hospital, also amplified allegations against Russian forces for international humanitarian law violations.

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Since the summer of 2022, most fighting has largely been confined to Ukraine’s east and south, with Russian cruise missiles, bombs, cluster munitions, and thermobaric weapons devastating port cities along the Black Sea and the Sea of Azov. The Russian seizure of several Ukrainian ports and subsequent blockade of Ukrainian food exports compounded an already acute global food crisis further exacerbated by climate change, inflation, and supply chain havoc. Prior to the conflict, Ukraine had been the largest supplier of commodities to the World Food Program (WFP), which provides food assistance to vulnerable populations. In July, Russia and Ukraine signed an agreement to free more than twenty million tons of grain from Russian-controlled Ukrainian ports. The first grain shipments to leave Ukraine since the Russian invasion departed from Odesa on August 1; they arrived in Russian-allied Syria on August 15, although their originally presumed destination had been Lebanon.

In mid-August, the southern shift of the war’s frontline sparked international fears of a nuclear disaster at the Zaporizhzhia nuclear plant along the Dnieper River. The largest nuclear plant in Europe, the Zaporizhzhia facility was seized by Russian forces in the earliest stages of the war. Escalating tensions between the plant’s Ukrainian staff and its Russian occupiers have also raised uncertainty regarding its continued safe operation. Fighting in the territory surrounding the facility also raises concerns that the plant could be critically damaged in the crossfire: shelling of the plant’s switchyard has already led to a city-wide black-out in Enerhodar, where the plant is located. Representatives of the International Atomic Energy Agency (IAEA), including Director General Rafael Mariano Grossi, visited the plant in early September to assess the threat of a nuclear accident. In a report [PDF] on the findings of its inspection, the IAEA called for “a nuclear safety and security protection zone” around the plant and for “all military activity” in the adjacent territory to cease immediately.

As of early September, Ukrainian forces have been able to make strong advances in the northeast and mounted a revitalized southern counteroffensive. Although Russia continues to hold onto much of Ukraine’s southeastern territory, Ukraine claims to have retaken significant territory in the Kharkiv region, surprising Russian forces and cutting off important supply lines. Russia has indicated that it plans to send reinforcements—about ten to twenty thousand soldiers—to the eastern front to combat the new Ukrainian offensive.

As of July 2022, the UN Human Rights Office has recorded over five thousand civilian deaths and over six thousand civilian injuries since Russia’s full-scale military invasion of Ukraine on February 24, 2022. The violence has internally displaced nearly seven million people and forced over six million to flee to neighboring countries, including Moldova and Poland, a NATO country where the United States and other allies are helping to accommodate the influx of refugees.

The U.S. continues to commit military assistance to Ukraine; following Ukrainian President Volodymyr Zelenskyy’s address to the U.S. Congress on March 16, 2022, Biden announced an additional $800 million in military assistance to Ukraine. Since Russia’s invasion, the United States has committed about $4.6 billion in security assistance, including heavy weapons and artillery, to the country. The United States has also dramatically increased U.S. troop presence in Europe, bringing the total to more than one hundred thousand. On September 8, 2022, U.S. Secretary of State Antony Blinken pledged continued support for Ukraine during a trip to Kyiv. While the United Nations, Group of Seven member states, EU, and others continue to condemn Russia’s actions and support Ukrainian forces, Russia has turned to countries like North Korea and Iran for intelligence and military equipment.

 Annexation of Ukrainian regions, escalating war

Amid patriotic pageantry hyped up by the fervor of war, Russian President Vladimir Putin on Friday proclaimed the annexation of four Ukrainian regions, a flagrant violation of international law that stands to escalate and prolong the military conflict in Ukraine, sharpen Moscow’s confrontation with the West and add to the Kremlin’s growing global isolation.

At a ceremony in the gilded Grand Kremlin Palace, attended by senior political and military officials, members of parliament and even Russian war bloggers, Putin on Friday signed so-called accession treaties to absorb the Ukrainian regions of Luhansk, Donetsk, Kherson and Zaporizhzhia.

The annexation move, while already rejected by President Biden, U.N. Secretary General António Guterres and other world leaders as unlawful and illegitimate, nonetheless laid Russia’s claim to some 40,000 square miles of land, or about one-seventh of all Ukrainian territory.

It was a momentous and remarkably brazen step — a land grab with virtually no parallel in modern times — and one with potentially dangerous consequences. Russia has warned that it would respond to any attacks on the seized Ukrainian territories as if they were Russia proper, potentially even with nuclear weapons.

The attempted seizure of territory, which Russian forces do not fully control either militarily or politically, also appeared to commit the country to a prolonged war. Ukrainian President Volodymyr Zelensky has pledged to fight until all of his country’s territory, including Crimea, is reclaimed, and Western allies have promised to send additional weapons and financial aid to support Kyiv in repelling the invaders.

Biden’s Additional Sanctions on Russia

Biden’s administration announced a new round of sanctions designed to tighten the access of Russia’s defense industry to technology and materials, and expanding penalties on Russian government officials and their family members, as well as Russian and Belarusian military officials.

Speaking at the White House after Putin’s signing ceremony at the Kremlin, President Biden said that “he’s not going to scare us or intimidate us. He can’t seize his neighbor’s land and get away with it.”

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The United States said it was sending a “clear warning” that there will be costs for any individual, entity or country that provides political or economic support to Russia. Three agencies — the Treasury, Commerce and State Departments — are imposing “swift and severe costs” on Russia, the administration said.

“Russia is violating international law, trampling on the United Nations Charter, and showing its contempt for peaceful nations everywhere,” Biden said. “Make no mistake: these actions have no legitimacy.”

He added: “The United States will always honor Ukraine’s internationally recognized borders. We will continue to support Ukraine’s efforts to regain control of its territory by strengthening its hand militarily and diplomatically.”

National security adviser Jake Sullivan, asked by reporters whether the latest sanctions — adding to numerous measures already imposed on Russian entities and individuals — would make a difference, said that they had three goals.


Last 24 Hours

Germany, Denmark and Norway to spend €92m on arms for Ukraine

Germany, Denmark and Norway have said they will spend €92m to buy 16 Slovak Zuzana-2 howitzers for Ukraine, the German defence ministry said.

The guns, which can fire six projectiles a minute over a distance of 40 km, will be built in Slovakia with delivery to begin next year, the ministry said.

Ukraine, which has scored notable battlefield successes against Russia in recent weeks, says it needs more and heavier armaments in order to repulse the invasion that Moscow launched in February.

Earlier we reported that Russia had struck the Ukrainian president's hometown of Kryvyu Rih in southern Ukraine with a suicide drone.

In recent weeks Russia has begun using Iranian-made suicide drones to attack targets in Ukraine.

'Kamikaze drones', which fly at a low altitude and explode on impact have been used in Ukraine.

UK to acquire specialist ships to protect underwater pipelines after 'sabotage' in Baltic Sea

 Ben Wallace says the government will acquire two specialist ships to protect underwater infrastructure such as cables and pipelines.

In remarks to the Conservative Party conference in Birmingham, the defence secretary referred to the "mysterious damage inflicted" last week following leaks in the Nord Stream gas pipelines in the Baltic Sea.

There have been suggestions that Russia could have been behind the alleged sabotage of the pipes, including Nord Stream 1 which was already shut but had previously pumped gas from Russia to Europe. Nord Stream 2 had not started operations.

Mr Wallace said the pipeline incident "should remind us of how fragile our economy and infrastructure is to such hybrid attacks".

"Our intent is to protect them. Our internet and energy are highly reliant on pipelines and cables. Russia makes no secret of its ability to target such infrastructure."

He went on: "So for that reason, I can announce we recently committed to two specialist ships with the capability to keep our cables and pipelines safe.

"The first multi-role survey ship for seabed warfare will be purchased by the end of this year, fitted out here in the UK and then operational before the end of next year.

"The second ship will be built in the UK and we will plan to make sure it covers all our vulnerabilities."

Russian military forces hit seven artillery and missile depots in Ukraine, says defence ministry says

The Russian military has hit seven artillery and missile depots in four of Ukraine's regions, according to the country’s defence ministry.

It claims that the strikes hit locations in Kharkiv, Zaporizhzhia, Mykolaiv and the Donetsk People’s Republic (DPR).

The ministry said the guidance radar for a S-300 air defence missile system had also been destroyed near Nova Kaluha in the Kherson region of southern Ukraine.

On Friday, Russian president Vladimir Putin proclaimed the annexation of Donetsk, Luhansk, Kherson and Zaporizhzhia, following referenda which have not been recognised by the West as legitimate. 

 Russian parliament to consider legal steps to absorb Ukrainian regions

Russia's parliament will consider on Monday bills and ratification treaties to absorb four Ukrainian regions, RIA Novosti news agency cited the speaker of Russia's lower house of parliament, Vyacheslav Volodin, as saying on Sunday.

On Friday, Vladimir Putin proclaimed Russia's annexation of a swathe of Ukraine in a Kremlin ceremony, promising Moscow would triumph in its "special military operation".

Russia declared the annexations of the regions - including Zaporizhzhia, home to Europe's largest nuclear power plant - after holding what it called referendums in occupied areas of Ukraine.

Western governments and Kyiv said the votes breached international law and were coercive and non-representative.

Separately the Russian Constitutional Court ruled on Sunday that the "international treaties" on the incorporation of the four regions to be in compliance with the Russian constitution.

The court also said the transition period on integration would last until 1 January 2026.

 Pope Francis calls for Putin to end 'spiral of violence and death'

Pope Francis has appealed to Russian president Vladimir Putin to end a "spiral of violence and death".

He made his strongest appeal yet on the seventh-month war as he addressed the public in St. Peter's Square. 

Pope Francis added that it is "absurd" that the world is facing a nuclear threat over Ukraine.

His comments follow recent remarks made by the Russian president who warned the West that he was not bluffing and would use "all the means" available if Russian territory is threatened. 

Concerns over the war heightened on Friday, when Mr Putin annexed four regions in Ukraine, following referendums denounced by the West as a sham.


Developments in the Russia-Ukraine conflict indicate frustrations in Russia. The last few weeks in September have been worse for Russia. First, a significant strategic defeat in Ukraine, after a stunning counteroffensive that dealt a blow to the Kremlin’s ambitions in the east. Then, what was supposed to be a gathering of likeminded leaders in Uzbekistan mostly served to remind him of his weakened status, as the Russian president was given short shrift by China and then chided by India. Meanwhile, in a neighborhood where Moscow is supposedly security guarantor, there has been fighting between Armenia and Azerbaijan, and clashes continue on the border between Kyrgyzstan and Tajikistan.

Putin is under pressure at home, too, with criticism from surprising corners. On Sunday, Alla Pugacheva, a much-loved pop singer who has been a household name for Russians for decades, posted a message criticizing “illusory aims” in Ukraine that have made Russia “a pariah” that weighs “heavily on the lives of its citizens.” On the other side, nationalists are furious at inept military leadership, forcing Kremlin spokesman Dmitry Peskov to warn that criticism would be fine — until it wasn’t: “The line is extremely thin. One should be very careful here.”

Yet it’s hard to avoid the reality of an unravelling campaign, and calls for national mobilization to solve all these concerns are growing too loud to ignore. Putin said last week that there was “no hurry” in Ukraine — his assumption clearly remains that the Russian regime can outlast Western resolve — and there would be no changes to the plan. But he made a point of saying Russia was "not fighting with a full army.”

For many, given the expansive goals at stake, that’s the problem. They argue Putin can’t win with his current strategy. National mobilization would add resources and manpower, widening the pool of fighters. But that’s theory. In practice, calling a spade a spade is all but unthinkable for the Kremlin, which still has no clearly articulated plan for Ukraine and has spent months separating ordinary Russians from reality on the frontline. Worst of all, it may already be too late, anyway.

For now, it’s certainly an unusually sonorous public discussion. In a rare outburst, former MP Boris Nadezhdin argued during a television talk show that it would be impossible to “beat Ukraine with these resources, with this ‘colonial war’ method, with contract soldiers, mercenaries and no general mobilization.” He added: “We either call for mobilization or go for a full-scale war, or we get out.” He suggested peace talks; other participants shouted him down.

Days later, Gennady Zyuganov, the head of Russia’s Communist Party and voice of the Kremlin-tolerated opposition, sought “maximum mobilization” and became the highest-profile figure to call the assault a war. “A war is something you can’t stop even if you want to,” he said in the Duma. “You have to fight to the end.”

For Zyuganov, security-forces hawks or figures like Ramzan Kadyrov, the pro-regime leader of the southern region of Chechnya whose militia is fighting in Ukraine, the benefit of mobilization is to add manpower and move the economy onto a war footing, focusing squarely on military production. But it’s an option that Putin, who depends on an illusion of stability and normalcy, is reluctant to take.

Three reasons come to mind. Most obviously, it would be an admission of failure. A special military operation that, seven months in, becomes a war, is hard to portray as a success.

Second, mobilization requires undoing the passivity on which Putin has built his regime. It involves galvanizing citizens who have largely been encouraged to sit out a war that was supposed to be surgical and swift. This was an assault that — unlike, say, the disastrous Soviet decade in Afghanistan — was supposed to be fought by paid volunteers, recruited from the country’s poorest (and often ethnically non-Russian) provinces, places like Tuva or Dagestan. Ordinary folks in larger cities could support a war that demanded nothing from them.

As Yuval Weber of Texas A&M's Bush School of Government and Public Service in Washington, DC put it, these masses in the middle are the real risk for the Kremlin, far more than the nationalist right. They are the ones on whom the regime has long relied, men and women who have been lulled into apathy but would now need to be whipped into a frenzy. More involved (and sending their own kin to war), they may well start asking awkward questions about Putin’s effectiveness. 

Then there’s the third problem — mass mobilization will be a huge challenge. The logistics are complex. The economy will not easily stomach the cost of losing workers, resistance to the draft is escalating and will only keep increasing as soldiers return from the front. Not to mention that men are needed now — but getting recruits through training will take months, given Russia does not have a strong, well-prepared reserve force. Nor is it clear how reservists and young conscripts, for now officially spared the frontline, can solve fundamental problems of leadership, morale and materiel.

And yet Russia can’t remain stuck fighting an existential war it has waged with too few men, losing them and their weapons at a staggering rate — US officials last month put the figure for killed or wounded since the start of the war at up to 80,000, though numbers vary widely.

There’s still danger that Russia could escalate, or use a supposedly growing threat to push through a declaration of war. As Ben Noble of University College London points out, increasing Kremlin talk of unprecedented NATO support for Ukraine may well be creating options for a regime that sees very few. The West, officials could eventually argue, forced Moscow’s hand.

But for now the Kremlin is betting on the next best thing — encouraging regions and mercenaries to mobilize on the state’s behalf, ignoring already deep coordination problems between fighting units.

Footage emerged last week of a man bearing a striking resemblance to sanctioned businessman Yevgeny Prigozhin addressing detainees in a prison on behalf of mercenary group Wagner, promising to commute sentences for service. “If you serve six months (in Wagner), you are free," he says. "If you arrive in Ukraine and decide it's not for you, we will execute you.”

Even more telling, though, was Prigozhin’s response on social media after the video went viral: “It’s either private military companies and prisoners, or your children,” he wrote. “Decide for yourself.”


President Vladimir Putin’s declaration of the annexation of four regions in eastern and southern Ukraine signals the onset of a new and highly dangerous phase in the seven-month war, one that Western officials and analysts fear could escalate to the use of nuclear weapons for the first time in 77 years.

Putin has previously threatened to resort to nuclear weapons if Russia’s goals in Ukraine continue to be thwarted. The annexation brings the use of a nuclear weapon a step closer by giving Putin a potential justification on the grounds that “the territorial integrity of our country is threatened,” as he put it in his speech last week.

He renewed the threat on Friday with an ominous comment that the U.S. atomic bombing of Hiroshima and Nagasaki created a “precedent” for the use of nuclear weapons, echoing references he has made in the past to the U.S. invasion of Iraq as setting a precedent for Russia’s invasion of Ukraine.

U.S. and Western officials say they still think it unlikely that Putin will carry out his threats. Most probably, they say, he is hoping to deter the West from providing ever more sophisticated military assistance to Ukraine while the mobilization of an additional 300,000 troops allows Russia to reverse or at least halt its military setbacks on the battlefield.

But the threats appear only to have strengthened Western resolve to continue sending weapons to Ukraine and the Ukrainian military is continuing to advance into Russian-occupied territory. On Saturday, the Ukrainian army seized control of the eastern city of Lyman in an area ostensibly annexed by Russia on Saturday.

The collapse of another Russian front line was greeted by calls for nuclear strikes by some military bloggers and political figures in Russia, including the Chechen leader Ramzan Kadyrov, a close ally of Putin. “More drastic measures should be taken, up to the declaration of martial law in the border areas and the use of low-yield nuclear weapons,” Kadyrov wrote in a comment on his Telegram channel.

In all four regions that Putin said he was annexing — Donetsk, Luhansk, Kherson and Zaporizhzhia — Russia only controls part of the territory.

Now that the areas being fought over are regarded by Moscow as Russian, it is possible to chart a course of events toward the first use of a nuclear weapon since the 1945 atomic bombing of Japan.

“It’s a low probability event, but it is the most serious case of nuclear brinkmanship since the 1980s” when the Cold War ended, said Franz-Stefan Gady, a senior fellow with the International Institute for Strategic Studies in London. “It is a very dangerous situation and it needs to be taken seriously by Western policymakers.”

U.S. and European officials say they are taking the threats seriously. White House national security adviser Jake Sullivan said on Sunday that there would be “catastrophic consequences” if Russia resorts to the use of nuclear weapons. He refused to specify what those would be but said the precise consequences had been spelled out privately to Russian officials “at very high levels.”

Now that the areas being fought over are regarded by Moscow as Russian, it is possible to chart a course of events toward the first use of a nuclear weapon since the 1945 atomic bombing of Japan.

“It’s a low probability event, but it is the most serious case of nuclear brinkmanship since the 1980s” when the Cold War ended, said Franz-Stefan Gady, a senior fellow with the International Institute for Strategic Studies in London. “It is a very dangerous situation and it needs to be taken seriously by Western policymakers.”

U.S. and European officials say they are taking the threats seriously. White House national security adviser Jake Sullivan said on Sunday that there would be “catastrophic consequences” if Russia resorts to the use of nuclear weapons. He refused to specify what those would be but said the precise consequences had been spelled out privately to Russian officials “at very high levels.”

European officials say the threats have only strengthened their resolve to support Ukraine.

“No one knows what Putin will decide to do, no one,” said a European Union official who spoke on the condition of anonymity to discuss a sensitive subject. “But he’s totally in a corner, he’s crazy … and for him there is no way out. The only way out for him is total victory or total defeat and we are working on the latter one. We need Ukraine to win and so we are working to prevent worst case scenarios by helping Ukraine win.”

The goal, the official said, is to give Ukraine the military support it needs to continue to push Russia out of Ukrainian territory, while pressuring Russia politically to agree to a cease-fire and withdrawal, the official said.

And the pressure is working, “slowly,” the official said, to spread awareness in Russia and internationally that the invasion was a mistake. India, which had seemed to side with Russia in the earliest days of the war, has expressed alarm at Putin’s talk of nuclear war and China, ostensibly Russia’s most important ally, has signaled that it is growing uneasy with Putin’s continuing escalations.

But the annexation and the mobilization of hundreds of thousands of extra troops have also served as a reminder that the Western strategy hasn’t yet worked enough to convince Putin that he can’t win, said Alexander Gabuev, a senior fellow with the Carnegie Endowment for International Peace who was based in Moscow until earlier this year.

The West had been hoping that Ukrainian successes would force Putin to back down, but instead he is doubling down. “Time and again we are seeing that Vladimir Putin sees this as a big existential war and he’s ready to up the stakes if he is losing on the battlefield,” Gabuev said.

“At the same time I don’t think the West will back down, so it’s a very hard challenge now. We are two or three steps away” from Russia failing to achieve its goals and resorting to what was once unthinkable.

Those steps to secure its positions include Russia pushing hundreds of thousands more men onto the battlefield; escalating attacks on civilian targets and infrastructure in Ukraine; and perhaps also embarking on covert attacks on Western infrastructure.

Although the United States and its European allies have refrained from making direct accusations, few doubt that Russia was behind the sabotage of the Nord Stream pipelines in the Baltic Sea, said the E.U. official.

“I don’t think anyone has doubts. It’s the handwriting of the Kremlin,” he said. “It’s an indication of, ‘look what is coming, look what we are able to do.’ ”

Nuclear weapons would only likely be used after mobilization, sabotage and other measures have failed to turn the tide, and it’s unclear what Putin would achieve by using them, Gady said.

Despite some wild predictions on Russian news shows that the Kremlin would lash out at a Western capital, with London appearing to be a favored target, it is more likely that Moscow would seek to use one of its smaller, tactical nuclear weapons on the battlefield to try to gain advantage over Ukrainian forces, said Gady.

The smallest nuclear weapon in the Russian arsenal delivers an explosion of around 1 kiloton, one fifteenth of the size of the bomb dropped on Hiroshima, which would inflict massive destruction but on a more limited area.

Because the war is being fought along a vast, 1,500-mile front line, troops are too thinly spread out for there to be an obvious target whose obliteration would change the course of the war. To make a difference, Russia would have to use several nuclear weapons or alternatively strike a major population center such as Kyiv, either of which would represent a massive escalation, trigger almost certain Western retaliation and turn Russia into a pariah state even with its allies, Gady said.

“From a purely military perspective, nuclear weapons would not solve any of Vladimir Putin’s military problems,” he said. “To change the operational picture one single attack would not be enough and it would also not intimidate Ukraine into surrendering territory. It would cause the opposite; it would double down Western support and I do think there would be a U.S. response.”

That’s why many believe Putin won’t carry out his threats. “Even though Putin is dangerous, he is not suicidal, and those around him aren’t suicidal,” said Ben Hodges, a former commander of U.S. Army Europe.

Pentagon officials have said they have seen no actions by Russia that would lead the United States to adjust its nuclear posture.