US President Joe Biden has called for Russian President Vladimir Putin to be tried for war crimes as evidence emerges of atrocities allegedly committed by Russian forces in Ukraine.
There is mounting international anger over the alleged killing of civilians in Bucha, a town near the capital Kyiv.
“This guy is brutal,” Mr Biden said of the Russian leader, adding that he believes Mr Putin “is a war criminal”.
Without evidence, Russia said images of atrocities had been staged by Ukraine.
US officials say they are supporting a team of international prosecutors heading to Bucha to collect evidence.
The Ukrainian government has started a war crimes investigation after it said the bodies of 410 civilians had been found in areas around Kyiv. Some were discovered in mass graves while others had their hands tied and had apparently been shot at close range.
Officials in Kyiv also accused Russian forces of killing a village head, her husband and her son in the village of Motoyzhyn for aiding Ukrainian troops in the area.
“You may remember I got criticised for calling Putin a war criminal,” Mr Biden said. “You saw what happened in Bucha – he is a war criminal… but we have to gather all the detail so this can have a war crimes trial.”
Mr Biden said the Bucha discovery was “outrageous” and said that it is important Mr Putin is “held accountable” for atrocities committed by his military Ukraine.
He added that he intends to seek to impose further sanctions on Russia.
Mr Biden’s intervention follows the publication of new satellite photos by the earth observation company Maxar, which showed bodies lining Bucha’s streets during its occupation by Russian forces.
An analysis of the photos by the New York Times showed at least 11 bodies on the streets on 11 March, when Russia occupied the city.
The US state department said it had credible reports of rape, torture and summary executions carried out by Russian forces as part of what it described as a “broader, troubling campaign” by Moscow.
At the request of Ukraine, the international prosecutors will support the prosecutor general of Ukraine’s war crimes unit.
“There are reports and images of a nightmare litany of atrocities,” said state department spokesman Ned Price.
The Pentagon said it was “fairly obvious” that Russia had been behind the atrocities in Bucha, but that more investigation was needed to ascertain which units were responsible.