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

The head of the Ukrainian nuclear power plant Zaporizhzhia has been released, after Ukrainian officials accused Russia of kidnapping him, according to the International Atomic Energy Agency.

Ihor Murashov, the head of the Zaporizhzhia nuclear power plant, was released and returned safely to his family, Rafael Mariano Grossi, the Director General of the IAEA, tweeted.

Zaporizhzhia is a Ukrainian facility now occupied by Russian troops.

Ukraine's nuclear power provider accused Russia on Saturday of "kidnapping" Murashov, according to the Associated Press.

Ukrainian state nuclear company Energoatom said Russian forces seized Murashov around 4 p.m. Friday. Energoatom said Russian troops stopped Murashov's car, blindfolded him and then took him to an undisclosed location, according to the AP.

Russian President Vladimir Putin's threats that his country could strike Ukraine with nuclear weapons were "irresponsible rhetoric" from a nuclear power, a Pentagon official said.

"They are continuing to be irresponsible rhetoric coming from a nuclear power," Pentagon spokesperson John Kirby said on "Good Morning America" on Monday. "There's no reason for him to use that kind of bluster, those kinds of threats."

But the U.S. was still taking the threats seriously, he said. The U.S. was "ready and prepared" to defend every inch of NATO territory, he said.

"We have to take these threats seriously. We must. It'd be easier if we could just blow it off, but we can't," Kirby said. "These are serious threats made by a serious nuclear power."

Russian officials are "likely struggling" to find officers and provide training for many of the reservists who've been called up as part of President Vladimir Putin's mobilization, the U.K. Ministry of Defense said.

"Local officials are likely unclear on the exact scope and legal rationale of the campaign," the ministry said in a Monday update. "They have almost certainly drafted some personnel who are outside the definitions claimed by Putin and the Ministry of Defence."

Some of the reservists are assembling in tented transit camps, the ministry said.

Former CIA chief David Petraeus said Sunday that Russian President Vladimir Putin has put himself in an "irreversible" situation amid the Kremlin's annexation of Russian-controlled Ukrainian regions.

"President Volodymyr co-anchor Jonathan Karl.

Petraeus said Putin "is losing" the war, despite "significant but desperate" recent moves. On Friday, Putin said he was annexing four regions of Ukraine -- a move denounced by Ukraine, the U.S. and other Western countries as a violation of international law -- and, in late September, the Russian leader said he was calling up some 300,000 reservists, triggering protests and a mass exodus from Russia.

In a rare acknowledgment Thursday, Putin admitted "mistakes" in how the country carried out the mobilization.