Joe Biden advises Americans to leave Ukraine as 'things could go crazy quickly'

But US president says if Putin were to invade, he's smart enough not to harm American citizens

People speak with a security guard outside the US embassy in Kiev on January 24. AFP

US President Joe Biden on Thursday urged American citizens to leave Ukraine, saying “things could go crazy quickly".

In an excerpt from an interview with NBC News, presenter Lester Holt asked Mr Biden under what circumstances might he send US troops into Ukraine to help Americans trying to flee.

“There’s not,” the president replied. “That’s a world war when Americans and Russia start shooting at one another. We’re in a very different world than we’ve ever been.”

He said that if Mr Putin was “foolish enough to go in, he’s smart enough not to, in fact, do anything that would negatively impact on American citizens".

Holt asked whether he has ever said that to Mr Putin, and the US president said he had. “I didn’t have to tell him that. I’ve spoken about that. He knows that."

In the interview, other parts of which will be broadcast on Friday and before the Super Bowl on Sunday, Mr Biden said, “American citizens should leave now.”

The State Department on Thursday cautioned against travel to the country because of “the increased threats of Russian military action and Covid-19. Those in Ukraine should depart now via commercial or private means".

"It's not like we're dealing with a terrorist organisation," Mr Biden said. “We’re dealing with one of the largest armies in the world. It’s a very different situation and things could go crazy quickly.”

Russia says it has no plans to invade Ukraine but wants the West to keep it and other former Soviet countries out of Nato.

It also wants Nato to refrain from sending weapons there and withdraw alliance forces from Eastern Europe.

The US and Nato flatly reject these demands.

News agencies contributed to this report