Biden calls to put Putin on trial for war crimes over Russia killings in Ukraine

President Joe Biden said Monday called for evidence to be gathered to put Russian leader Vladimir Putin on trial for war crimes related to his nation's invasion of Ukraine.

"He is a war criminal," Biden said of Putin, on the heels of reports of mass killings of civilians by Russian-controlled troops in the town of Bucha, northwest of Ukraine's capital of Kyiv.

"This guy is brutal, and what's happening in Bucha is outrageous and everyone's seen it," Biden told reporters.

"I think it is a war crime ... He should be held accountable."

Biden also said that he plans to slap additional sanctions on Russia for its conduct during the war, which began with an invasion on Feb. 24.

"I'll let you know," the president replied when a reporter asked him the nature of those expected sanctions.

Ukrainian President Volodymyr Zelenskyy earlier said that Russian forces of committing genocide, with Ukrainian people being "destroyed and exterminated."

Bucha's mayor has said about 300 residents of the town had been killed at the time that fighters from Chechnya controlled the area.

Russia has denied allegations that its troops killed civilians in Bucha.

Biden said Monday, "You may remember, I got criticized for calling Putin a war criminal" last month.

"Well, the truth of the matter, you saw what happened in Bucha. This warrants him — he is a war criminal," Biden said.

"But we have to gather the information. We have to continue to provide Ukraine with the weapons they need to continue the fight," the president said.

"We have to get all the detail so this can be ... a war crime trial."