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

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."

U.S. Secretary of State Antony Blinken spoke via telephone with his Ukrainian counterpart, Dmytro Kuleba, on Sunday "to reaffirm the United States' steadfast support for Ukraine's sovereignty, independent, and territorial integrity," according to a statement from U.S. Department of State spokesperson Ned Price.

"Secretary Blinken expressed to Foreign Minister Kuleba that the United States rejects Russian Defense Minister Shoygu's transparently false allegations that Ukraine is preparing to use a dirty bomb on its own territory and that the world would see through any attempt by Russia to use this allegation as a pretext for escalation," Price said.

"They also discussed the U.S. and international commitment to continue supporting Ukraine with unprecedented security, economic and humanitarian assistance for as long as it takes, as we hold Russia accountable," he added. "They further noted our ongoing efforts to manage the broader implications of President Putin's war."

Russian Minister of Defense Sergey Shoigu called his counterparts in Turkey, France and the United Kingdom on Saturday, claiming that Ukraine is preparing a provocation with the use of a "dirty bomb."

The first mention of a possible Ukrainian "dirty bomb" attack appeared Sunday in a morning message of the RIA Novosti state-owned news agency. The article, citing "credible sources in various countries, including Ukraine," stated that "the Kiev regime is preparing a provocation on the territory of its country related to the detonation of the so-called 'dirty bomb' or low-power nuclear munition."

"The purpose of the provocation is to accuse Russia of using weapons of mass destruction in the Ukrainian theater of operations and thereby launch a powerful anti-Russian campaign in the world aimed at undermining confidence in Moscow," RIA Novosti reported.

Shoigu also had a telephone conversation with the U.S. Secretary of Defense Lloyd Austin on Sunday, during which they discussed the situation in Ukraine, according to a Pentagon official.

"Secretary Austin rejected any pretext for Russian escalation and reaffirmed the value of continued communication amid Russia’s unlawful and unjustified war against Ukraine," said Pentagon press secretary, Brig. Gen. Pat Ryder.