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Russia’s Claims of a ‘Dirty Bomb’ in Ukraine Spark Fears About What Putin Is Planning Next

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A series of allegations and actions by Russia on Monday sparked fresh fears in Washington that President Vladimir Putin was considering escalating his bloody war in Ukraine.

Without providing any evidence, the Kremlin publicly alleged that Ukraine was planning to detonate an explosive device mixed with radioactive material on its own territory with the intention of blaming Moscow. The Russian Defense Ministry said its forces were being prepared to operate in conditions of radioactive contamination due to threats of this purported attack using such a device, colloquially called a “dirty bomb.”

The allegations were roundly dismissed in Kyiv, Washington and European capitals, where leaders warned that Moscow was attempting to create a pretext for its own escalation, possibly carrying out a so-called “false-flag” operation that would inflict mass casualties and environmental contamination. It is a well-established Kremlin tactic to launch devastating attacks and then blame its enemies for the casualties. “If Russia calls and says that Ukraine is allegedly preparing something, it means one thing: Russia has already prepared it,” said Ukrainian President Volodymyr Zelenskyy in a video address.

The White House on Monday expressed concern regarding Russia’s dirty bomb claims and rejected the notion that Kyiv was preparing such an attack. “There is no plan by the Ukrainians to do this, so, of course, that gives us concern and we’re obviously taking the issue seriously,” National Security Council spokesman John Kirby told reporters. “All I can assure you is that we are taking it seriously and we are monitoring as best we can.”

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Detonation of a dirty bomb has been a top U.S. government concern for decades. Until now, the fear has centered on a terrorist obtaining highly radioactive materials—from a hospital for medical imaging or other scientific purposes—and packing it around an explosive charge. The force of the initial blast would be only as deadly as that of a conventional bomb, but the scattering of radioactive debris would be even more deadly and could injure victims with radiation poisoning. Because the technical challenge doesn’t involve splitting an atom, the bombs are easier to construct. The devices are small—potentially fitting in a suitcase, for instance, and still capable of contaminating several city blocks. A 2004 study conducted by the National Defense University found that the economic impact of a dirty bomb could exceed those incurred after the 9/11 attacks.

The White House said the U.S. would be able to detect preparations for the staging of dirty bomb attack through reconnaissance satellites, communication intercepts and other intelligence instruments, but acknowledged there would be challenges to how much advance warning they would be able to provide. “A lot of our ability to detect would be determined by a range of factors including the length of time that the perpetrators prepare for communications” and the time involved in building such a device, Kirby said. “When I say we are not seeing any preparations, it’s that we are not seeing any physical preparations.”

It’s unclear what, if any, use a dirty bomb would have on the battlefield. Pavel Podvig, a senior researcher at the UN Institute for Disarmament Research in Geneva, noted that Russian officials have repeatedly warned that Ukraine was preparing a weapon of mass destruction—even before their unprovoked Feb. 24 invasion. At various points throughout the year Moscow has falsely alleged that Ukraine was: seeking a stockpile of its own nuclear warheads; used botulinum toxin to poison Russian soldiers; and operated a network biological weapons laboratories with U.S. support. The dirty bomb claim “seems to be a claim on par with the ‘biolabs’ accusations—create a lot of innuendo and muddy the waters,” Podvig says. “And, of course, a bonus is that anything nuclear-related makes people nervous.”

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It’s possible that Russia is considering a “false-flag” operation by leveling these accusations in such a public manner, but Moscow could also be trying to lay the groundwork for their own escalation, says Olga Oliker, the International Crisis Group’s director for Europe and Central Asia. “Perhaps they also just wanted to plant more doubts about Ukraine in the global press, as well as more concerns about the risk of escalation in this war,” she says.

On Monday, the Russian Defense Ministry took to Telegram to outline how Ukraine maintained the scientific and industrial capabilities to create a dirty bomb. Ukrainian Defense Minister Oleksii Reznikov said Moscow was engaging in “nuclear blackmail,” inviting international monitors to see for themselves that his forces had no such plans.

The post came a day after Russian Defense Minister Sergei Shoigu made a flurry of phone calls with his counterparts in France, Britain, Turkey and the U.S. about the alleged coming dirty bomb attack. The Western governments issued a joint statement late Sunday, which dismissed Russia’s transparently allegations. “The world would see through any attempt to use this allegation as a pretext for escalation,” the statement said.

The Institute for the Study of War, a non-profit think tank in Washington, assessed that Russia was “unlikely to be preparing an imminent false-flag dirty bomb attack,” but has warned that Russian forces may be planning another covert operation by blowing up a hydroelectric dam in southern Ukraine. If an attack on the dam did take place, it would flood areas around the southern region of Kherson, cut water supplies to people living there and threaten the cooling system for Europe’s largest nuclear plant.

General Sergei Surovikin, Russia’s new chief commander in Ukraine, warned last week that Ukraine could attack the dam and imperil his troops, many of whom are retreating from Kherson. The retreat is just one of several embarrassing military setbacks for Moscow. In response, the Russian military has unleashed missile and drone strikes on energy plants and civilian targets, triggering fears that hostilities were escalating and inching the world closer to the brink of nuclear war.

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Write to W.J. Hennigan at william.hennigan@time.com