US President Joe Biden speaks during an event in Washington. File photo

The president spoke out in a rare televised interview as his administration looks for what he has described as an "off-ramp" for Putin to deescalate his invasion of Ukraine before he resorts to weapons of mass destruction.

"I think he is a rational actor who has miscalculated significantly," Biden told CNN after Moscow's shelling of civilian targets across its neighbor marked an escalation in the seven-month conflict.

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Biden warned last week that the world risks "Armageddon" in unusually direct remarks about the dangers from Putin's thinly veiled threats to use nuclear weapons to assist Russia's faltering attempt to take over swaths of Ukraine.

Russian President Vladimir Putin attends a meeting. File photo

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.

Biden told CNN that while he believed Putin was rational, he had underestimated the ferocity of Ukrainian defiance.

"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.

The president even left open the possibility of talks with his Russian counterpart on the sidelines of the meeting of G20 nations in Bali scheduled for November -- although he was clear there are no plans for talks on Ukraine.

"Look, I have no intention of meeting with him," Biden told CNN, adding that he would however see Putin if the Russian leader wanted negotiations over releasing detained US basketball star Brittney Griner.

"If he came to me at the G20 and said 'I want to talk about the release of Griner,' I'd meet with him. I mean, it would depend," he said.

Agence France-Presse