Ukrainian President Volodymyr Zelenskyy on Sunday denied claims by Russian Defense Minister Sergei Shoigu that Ukraine is planning to deploy a "dirty" bomb on its own people, arguing that only Russia is capable of using nuclear weapons in Europe.

Shoigu on Sunday held talks with U.S. Defense Secretary Lloyd Austin for the second time in three days since May and spoke with three counterparts from NATO countries, which Zelenskyy referred to as a "phone carousel."

"When today the Russian Minister of Defense organizes a phone carousel," Zelenskyy wrote via Telegram, "and calls foreign ministers with stories about the so-called 'dirty' nuclear bomb, everyone understands everything well. Understands who is the source of everything dirty that can be imagined in this war."

"And there's only one subject who can use nuclear weapons in our part of Europe, and this subject is the one who ordered comrade Shoigu to call somewhere," the Ukrainian president added, alluding to Russia. "I believe that now the world should react in the toughest possible way."

Before Zelenskyy's Sunday evening address, Shoigu, according to Reuters, spoke with U.S. Secretary of Defense Austin. Shoigu also expressed to other world leaders, according to Moscow, how the situation in Ukraine is worsening.

French Defense Minister Sebastien Lecornu and Shoigu "discussed the situation in Ukraine which is rapidly deteriorating," the Russian defense ministry said. "It is trending towards further uncontrolled escalation."

Shoigu also reportedly spoke separately to Britain's defense minister, Ben Wallace, and Turkish Defense Minister Hulusi Akar.

During his talks with Britain, Turkey, and France, Shoigu expressed concern that Ukraine was prepared to unleash a "dirty" bomb laced with nuclear material in its own territory. So far, no evidence or reports back this claim.

As Reuters adds, "previous Russian assertions that Ukraine might resort to using banned weapons such as biological arms have stirred concerns in the West that Moscow might be preparing to stage 'false flag' attacks and blame them on Kyiv."

According to the Pentagon, Austin told Shoigu he "rejected any pretext for Russian escalation" in Ukraine but also "reaffirmed the value of continued communication" with the West.

Additionally, the White House National Security Council echoed the Pentagon's position stating it rejects Shoigu's allegations that Ukraine is preparing to use a dirty bomb on its territory.

"The world would see through any attempt to use this allegation as a pretext for escalation," the White House stated.

While there is no indication the conversations produced any positive steps toward diplomacy, they did reveal that Russia and members of NATO are actively preserving channels of communication at a time of rising anxiety amidst escalation toward nuclear conflict.

After Shoigu's call on Friday with Austin, a top Russian diplomat was quoted as saying that "misunderstandings must be cleared up so that there are no accidents."

France's Lecornu said he had reaffirmed his country's desire for a peaceful resolution to the war and that Paris refused to get drawn into any escalation.

But Britain said Wallace "refuted" Shoigu's claims that Western countries were facilitating a plan by Kyiv to escalate the conflict.

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