“The Pentagon didn’t have to be asked,” Biden said in an interview on Tuesday with CNN, in response to a question about whether he’d directed the Defence Department to come up with contingencies.

The president declined to elaborate on the discussions, saying it would be irresponsible “to talk about what we would or wouldn’t do”.

At a political fundraiser last week, Biden expressed concern that Putin could escalate further, saying the world faced “the prospect of Armageddon” if Putin used nuclear weapons in the conflict. US officials later said there is no intelligence indicating Russia is preparing a nuclear attack.

Biden said on Tuesday that his comments were directed toward Putin himself and that he ultimately doesn’t think the Russian leader would go through with deploying a nuclear weapon.

“I don’t think he will. But I think that it’s irresponsible for him to talk about it,” he said. “Once you use a nuclear weapon, the mistakes that can be made, the miscalculations, who knows what will happen?”

Biden also said last week that the US is trying to find an “off-ramp” for Putin to bring an end to the conflict. On Tuesday, he suggested Putin could just abandon his efforts in Ukraine.

“I don’t know what’s in his mind. But clearly, he could leave. He could just flat leave and still probably hold his position together in Russia,” Biden said.

Biden’s comments came after a deadly Russian missile barrage on Monday against Kyiv and other cities that damaged key infrastructure and civilian sites. Biden and his allies are facing renewed pressure to supply Ukraine with sophisticated weaponry they have thus far been reluctant to provide, following Russia’s steps to escalate the war.

Ukrainian President Volodymyr Zelenskiy said after a call with Biden on Monday that air defences were his number one priority, and the US president said he would be willing to provide “advanced” equipment to meet those needs.

The Group of Seven major industrialised nations held an emergency call with Zelenskiy on Tuesday to discuss their response to the Russian attacks. The allies pledged in a statement to support Ukraine “for as long as it takes”.

Biden on Tuesday described Putin as a “rational actor” who has “miscalculated significantly” when he decided to invade.

But elsewhere in the interview, the president characterised the Russian leader’s decision to invade as irrational.

“He talked about the whole idea of – he was needed to be the leader of Russia that united all Russian speakers. I mean, it’s just I just think it’s irrational,” Biden said in the interview.

He added that Putin “thought he was going to be welcomed with open arms, that this was the home of Mother Russia in Kyiv, and that where he was going to be welcomed, and I think he just totally miscalculated”.