Russia-Ukraine updates: Putin suspends key US-Russia nuclear treaty in speech denouncing West

A senior commander of the Russian military said Monday that his troops have been readied to operate "in the conditions of radioactive contamination," amid Moscow's allegation that Ukraine is preparing to use a "dirty bomb" on its own territory.

"Work has been organised by the [Russian] Ministry of Defense for combating possible provocations from the side of Ukraine: forces and equipment have been put in readiness for fulfilling tasks in the conditions of radiative contamination," Kirillov said during a press briefing, as quoted by Russian state media.

The comments are further worrying signs that Russia is trying to build a false-flag narrative, blaming Ukraine for the possible use of nuclear weapons, which is clearly intended as a threat to both Ukraine and its Western allies.

-ABC News’ Patrick Reevell

Russia responded on Monday to a joint statement from the United States, the United Kingdom and France rejecting Moscow's "transparently false allegations" that Ukraine is preparing a provocation with the use of a "dirty bomb" on its own territory.

"The thing is that their mistrust toward the information shared by Russia doesn't mean that the threat of the use of such a dirty bomb ceases to exist," Kremlin spokesman Dmitry Peskov said during a press briefing. "The threat is obvious. This information was shared by the defense minister with his counterparts, and now it is up to them to believe or not believe in it."

The commander of the Ukrainian Ground Forces warned that Russian President Vladimir Putin's threat to use nuclear weapons in Ukraine is real and that the West "should be worried," but said his country is nonetheless winning the war.

Gen. Col. Oleksander Syrskiy made the comments in an exclusive interview with ABC News' Chief Foreign Correspondent Ian Pannell in the eastern Ukrainian city of Kharkiv on Sunday. As the 57-year-old top commander of his country's land forces, Syrskiy has played a decisive role in turning the war in Ukraine's favor, first leading the successful defense of the capital, Kyiv, and then -- most recently -- masterminding the spectacular counteroffensive in the northeast that upended the monthslong conflict and threw Russian forces onto the defensive.

The rare interview, airing Monday on "Good Morning America," is one of the few times Syrskiy has spoken publicly at length and he described Ukraine's tactics, the importance of Western support, the threat of renewed attacks from Belarus and his determination that Ukraine will reclaim all of its territory, including the Moscow-annexed Crimean Peninsula.

Ukraine's successes, however, have been shadowed by the recent threats from Putin that Russia might resort to nuclear weapons to reverse the course of his war in Ukraine. Syrskiy told ABC News that he takes the threats seriously.

"We are and should be worried," Syrskiy said. "I do believe that such a threat really exists and we have to take it into account."

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Ukrainian general on Putin’s nuclear threat: 'We are and should be worried'The commander of Ukraine's ground forces, Gen. Oleksandr Syrskiy, tells ABC News' Ian Pannell the world should be worried about Russian President Vladimir Putin's threat to use nuclear weapons.

ABCNews.com

The governments of the United States, the United Kingdom and France released a joint statement on Sunday rejecting "Russia's transparently false allegations that Ukraine is preparing to use a dirty bomb on its own territory."

"We, the Foreign Ministers of France, the United Kingdom, and the United States, reiterate our steadfast support for Ukraine's sovereignty and territorial integrity in the face of Russia's ongoing aggression," they said in the joint statement. "We remain committed to continue supporting Ukraine's efforts to defend its territory for as long as it takes."

"Earlier today, the defense ministers of each of our countries spoke to Russian Defense Minister Sergei Shoygu at his request," they continued. "Our countries made clear that we all reject Russia's transparently false allegations that Ukraine is preparing to use a dirty bomb on its own territory. The world would see through any attempt to use this allegation as a pretext for escalation. We further reject any pretext for escalation by Russia."

They added: "The Foreign Ministers also discussed their shared determination to continue supporting Ukraine and the Ukrainian people with security, economic, and humanitarian assistance in the face of President Putin's brutal war of aggression."