Britain's Prime Minister Boris Johnson has dismissed Vladimir Putin's announcement he is putting Russia's strategic nuclear forces on high alert as a "distraction" from the struggle his troops are facing in Ukraine.
The Russian leader said on Sunday he was putting Moscow's nuclear forces on a "special regime of combat duty" in response to "aggressive statements" coming from Western powers.
But Mr Johnson has suggested Mr Putin's actions were more to do with the fact his forces were meeting with "more resistance than the Kremlin had bargained for".
He also cast doubt on possible negotiations between Russian and Ukrainian delegations to try to resolve the crisis.
Ukraine President Volodymyr Zelenskyy agreed the two sides could meet on the Ukraine-Belarus border having initially rejected an offer of talks in Belarus.
However Mr Johnson said he had seen nothing to suggest Mr Putin was genuine in his offer.
"There's nothing I've seen so far in his behaviour that leads me to think that he could possibly be sincere," the British PM said.
Earlier, Russian television footage showed Mr Putin meeting with his defence minister and the chief of the general staff, and instructing them to ready the nation's nuclear forces.
"Western countries aren't only taking unfriendly actions against our country in the economic sphere, but top officials from leading NATO members made aggressive statements regarding our country," he said.
But on a day when the expected assault on Kyiv again failed to materialise and the Ukrainians claimed to have driven Russian forces out of the country's second city Kharkiv, Mr Johnson said Mr Putin's words were "a distraction from the reality of what's going on".
"This is an innocent people who are facing a totally unprovoked act of aggression against them, and what's actually happening is that they are fighting back perhaps with more effect, with more resistance, than the Kremlin had bargained for," he said.
"You can see some of the logistical difficulties that the Russian forces are experiencing.
"The Russian defence ministry have themselves conceded that they're having casualties.
"This is a disastrous misbegotten venture by President Putin."
The United States and NATO have also condemned Mr Putin's order to put his nuclear forces on high alert as dangerous and unacceptable.
The US ambassador to the United Nations, Linda Thomas-Greenfield, told CBS's Face the Nation program that Mr Putin's actions have escalated the conflict and were "unacceptable".
Ms Thomas-Greenfield said the US was "continuing to look at new and even harsher measures against the Russians".
On CNN's State of the Union program, NATO Secretary-General Jens Stoltenberg called Mr Putin's nuclear order "aggressive" and "irresponsible".
White House Press Secretary Jen Psaki said Mr Putin was responding to an imaginary threat.
"We've seen him do this time and time again. At no point has Russia been under threat from NATO, has Russia been under threat from Ukraine," Ms Psaki said on ABC's "This Week" program.
