US says Russia's 'dirty bomb' claims are pretext for escalation in Ukraine

U.S. officials are flatly rejecting as false repeated Russian claims being made to senior western officials that Ukraine is preparing to use a radioactive "dirty bomb" in Ukraine, saying at the same time they are not seeing any indications that Russia is preparing to use nuclear weapons.

In this weekend's phone calls to top officials at the Pentagon, Russian military leaders indicated that the alleged Ukrainian use of a dirty bomb would be a justification for an escalation in the conflict, a U.S. official told ABC News.

Over the weekend, in an unprecedented series of phone calls to senior defense officials in the United States, the United Kingdom, France, and Turkey, senior Russian defense officials repeatedly claimed that Ukraine was possibly preparing to use a dirty bomb.

A dirty bomb is an explosive device paired with radioactive material that is intended to widely disperse radiation over a wide area while a nuclear weapon is a device that uses nuclear fission to produce a massive atomic or thermonuclear explosion.

"Obviously, we're concerned about these allegations that the Russians raised, them, not us," John Kirby, the National Security Council Coordinator for Strategic Communications told reporters on Monday. "They're the ones that made a public issue of this."

"We reject the false allegation that the Russians made in the phone call that they placed at their request to (Defense) Secretary Austin, that the Ukrainians were planning to use a dirty bomb," said Kirby. "We just reject that allegation. It's just not true."

On Sunday and Monday, in a rare move, Russian defense minister Sergey Shoygu and Russia's top military commander Gen. Valery Gerasimov initiated phone calls to their American counterparts and, according to Russia's defense ministry, raised their concerns that Ukraine was preparing to use a dirty bomb.

Those calls, and similar calls to other western leaders, resulted in a joint statement by the United States, the United Kingdom, and France rejecting the Russian claim as a pretext to escalate tensions in Ukraine.

"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," said the statement. "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."

A U.S. official said that, in this weekend's calls to top officials at the Pentagon, Russian military leaders described any alleged Ukrainian use of a dirty bomb as a justification for an escalation in the conflict, presumably a reference to the use of nuclear or chemical-biological weapons.

However, U.S. officials pointed out repeatedly on Monday that they are not seeing any indications that Russia's military is making preparations for the use of nuclear weapons.

"We continue to see nothing in the way of preparations by the Russian side for the use of nuclear weapons and nothing with respect to the potential use for a dirty bomb at this point," said Kirby. "We're watching this as closely as we can."

"We have seen in the past that the Russians have, on occasion, blamed others for things that that they were planning to do," said Kirby.

Meanwhile in Moscow, the Russian government continued to say that Ukraine was preparing to use a dirty bomb.

Russian Foreign Ministry spokesperson Maria Zakharova claimed that Russia was in possession of information alleging that Ukraine was preparing dirty bombs at locations in Kyiv and central Ukraine.

Earlier, the Russian defense ministry had published a map indicating that Ukraine was preparing a dirty bomb at the Zaporizhzhia nuclear power plant that has seen constant shelling for weeks.