Washington (AFP) - The United States said Wednesday that public information and intelligence it has collected amounts to strong evidence that the Russian military has committed war crimes in Ukraine.

The announcement came as Russian forces continued to bombard the southern Ukraine city of Mariupol, where the bombing of a maternity hospital and a theater where hundreds of civilians had taken refuge have sparked global outrage.

"Today, I can announce that, based on information currently available, the US government assesses that members of Russia's forces have committed war crimes in Ukraine," Secretary of State Antony Blinken said in a statement.

Since the Russians first invaded on February 24, Blinken said, "We've seen numerous credible reports of indiscriminate attacks and attacks deliberately targeting civilians, as well as other atrocities."

The US assessment that war crimes were committed, he said, "is based on a careful review of available information from public and intelligence sources."

"We are committed to pursuing accountability using every tool available, including criminal prosecutions," he said.

Mariupol theater bombing

Blinken did not enumerate specific cases that the United States had concluded amounted to war crimes.

But he singled out the devastation of Mariupol in his announcement.

"As of March 22, officials in besieged Mariupol said that more than 2,400 civilians had been killed in that city alone," he said.

Blinken said that many sites struck by Russian forces were clearly identifiable as being used by civilians.

Those include the Mariupol maternity hospital where three people died, including a child, in a Russian strike on March 9.

"It also includes a strike that hit a Mariupol theater," where the Russian word for "children" had been marked out on the ground in huge letters clearly visible from the sky, Blinken said.

Hundreds of people were said by city officials to have been sheltering in the theater when it was bombed on March 16. 

So far no deaths have been reported, but days afterwards officials were still removing rubble.

Blinken also cited a UN estimate that 2,500 civilians had been killed or wounded elsewhere in Ukraine since the month-old war began.

International Criminal Court

Beth Van Schaack, the newly appointed US Ambassador-at-Large for Global Criminal Justice, said that the US is collecting evidence for submission to any war crimes proceedings that could be launched in the wake of the war.

"This is going to be an ongoing process throughout this conflict," she said.

Cases could be presented in venues ranging from Ukraine's courts, to countries in the region that might take custody over alleged perpetrators, or which might be able to conduct in absentia trials.

She also said the International Criminal Court could be a key venue, despite Washington's refusal to ratify the institution.

"We welcome the fact that the new incoming prosecutor of the International Criminal Court has also opened an investigation into the situation within Ukraine," Van Schaack said.

She said the Mariupol theater case was "extremely important." 

"It appears to have been a direct attack upon a civilian object," she said.

Could Putin be charged?

She also said that law on war crimes allows charges to be made against people in command positions.

"The doctrine of superior responsibility allows for commanders to be held responsible for acts committed by their subordinates," she said.

Asked if that could include Russian President Vladimir Putin, Van Schaack replied "yes."

"There are doctrines under international law and domestic law that are able to reach all the way up the chain of command," she said.