Joe Biden has said he believes Vladimir Putin is a “rational actor” who badly misjudged his prospects of occupying Ukraine, but does not believe he would resort to using a tactical nuclear weapon.

The US president told CNN in remarks released ahead of a rare TV interview on Tuesday that he believed his Russian counterpart had underestimated the ferocity of Ukrainian defiance in the face of invasion.

“I think … he 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,” Biden said.

“I think he is a rational actor who has miscalculated significantly.”

When asked by interviewer Jake Tapper how realistic he believed it would be for Putin to use a tactical nuclear weapon, Biden responded: “Well, I don’t think he will.”

The president spoke as his administration looks for what he has described as an “off-ramp” for Putin to de-escalate his invasion of Ukraine before he resorts to weapons of mass destruction.

Biden warned last week that the world risks “Armageddon” in unusually direct remarks about the dangers posed by Putin’s thinly veiled threats to use nuclear weapons to assist Russia’s faltering attempt to take over swathes of Ukraine.

Putin’s state of mind has been the subject of much debate after the Russian president suffered a series of recent military set-backs in the invasion, which he launched in February.

On Tuesday, Biden suggested that he believed Putin to be rational overall but questioned the language used when announcing the invasion of Ukraine back in February.

“If you listen to the speech he made after, when, that decision was being made, he talked about the whole idea of – he needed to be the leader of Russia that united all of Russian speakers. I mean, it’s just, I just think it’s irrational,” Biden said.

Biden’s remarks were released after Ukraine’s president, Volodymyr Zelenskiy, asked G7 leaders for more air defence systems and a monitoring mission on the Belarusian border, as Russia continued to attack key infrastructure in Ukraine with a new wave of missile strikes.

In response to Zelenskiy’s speech, G7 leaders issued a statement saying they would “stand firmly with Ukraine for as long as it takes”.

In a separate video address on Tuesday night, Zelenskiy said: “The enemy launched a second wave of terrorist attacks against our country. As of this morning, there were 28 missiles, of which 20 were shot down. More than 15 drones, almost all of them are Iranian combat drones. Most were shot down.”

The White House national security council spokesperson, John Kirby, said on Tuesday the US was working to expedite the shipment of Nasams air defences capable of engaging Russian cruise missiles. Germany’s Der Spiegel magazine reported on Tuesday that Ukraine had received a delivery of the German Iris-T air defence system.

With Agence France-Presse