US President Joe Biden has called Russian President Vladimir Putin a war criminal as the atrocities in Ukraine mount and the president there begged the US Congress for more help.

"He's a war criminal," Biden said of Putin as he left an unrelated event.

It is the sharpest condemnation yet of Putin and Russian actions by a US official since the invasion of Ukraine.

While other world leaders have used the words, the White House had been hesitant to declare Putin's actions those of a war criminal, saying it was a legal term that required research.

But in a speech on Wednesday, Biden said Russian troops had bombed hospitals and held doctors hostage.

He pledged more aid to help Ukraine fight Russia.

© AP 2022