The United States has assessed that members of Russia's forces have committed war crimes in Ukraine, US Secretary of State Antony Blinken says, adding that Washington's conclusion is based on a "careful review" of available information from public and intelligence sources.
Mr Blinken said there had been "numerous credible reports of indiscriminate attacks and attacks deliberately targeting civilians, as well as other atrocities" by Russia's forces in Ukraine, specifying attacks in the besieged city of Mariupol.
Russia has denied targeting civilians.
In a statement, Mr Blinken said the United States would continue to track reports of war crimes and share information it gathered with allies and international institutions.
A court of law would be ultimately responsible in determining any alleged crime, he said.
US President Joe Biden last week said Russian President Vladimir Putin was "a war criminal" for attacking Ukraine, which Russia's foreign ministry said was a statement "unworthy of a statesman of such high rank".
Moscow has yet to capture any of Ukraine's biggest cities since launching its invasion on February 24, the largest assault on a European state since World War II.
Putin calls his offensive a "special military operation" to demilitarise and "de-Nazify" the country.
The civilian casualties are thought to be in the thousands while the United Nations estimates more than 3.5 million people have fled.
Investigators from the International Criminal Court set off earlier this month to start looking into possible war crimes in Ukraine.
Washington has welcomed the move, although it has no cooperation duties since it is not a member of the court.
Beth Van Schaack, ambassador-at-large for Global Criminal Justice at the State Department, said Washington was looking at the broad range of activities that Russia's forces were engaged in within Ukraine.
The destruction of a theatre in Mariupol last week "appears to have been a direct attack upon a civilian [target]", she said.
"This was very clearly marked with the word 'children' … It's not a military objective," she said at a briefing at the State Department.
Russia has denied bombing the theatre.
Ms Van Schaack said evidence such as signals intelligence and accounts from Russian insiders could be used by courts to show that civilians were intentionally targeted.
Such evidence was being preserved for that purpose, she said.
Legal experts say a prosecution of Mr Putin or other Russian leaders would face high hurdles and could take years.
Retaliation as US expels diplomats
The United States embassy in Moscow on Wednesday received a list of its diplomats that were declared "persona non grata", a State Department spokesperson said, in what Russian media said was a response to a US move ousting Russian staff at the United Nations.
Washington last month said it was expelling 12 Russian diplomats at the country's UN mission in New York over national security concerns, and later announced it would oust an additional Russian at the UN who it said was a spy.
Russia, which denies the allegations, told the United States on Wednesday it would throw out an unspecified number of American diplomats in response to the moves, Interfax news agency said.
"The American side was told very firmly that any hostile US actions against Russia would provoke a decisive and comparable response," the agency said.
The move comes as the United States and its allies weigh further sanctions against Russia over its invasion of Ukraine.
"This is Russia's latest unhelpful and unproductive step in our bilateral relationship … Now more than ever, it is critical that our countries have the necessary diplomatic personnel in place to facilitate communication between our governments," the spokesperson said.
What is Australia saying?
Australia has joined the United States' government in labelling Russia's attacks on civilian areas in Ukraine as war crimes.
"The intentional targeting of civilians is a war crime, the bombing of civilian infrastructure, targeting schools where civilians are sheltering … targeting air strikes onto a theatre where civilians were known to be sheltering, bombing maternity hospitals … is a war crime," Australia's Foreign Minister, Marise Payne, said.
Senator Payne says the federal government is keeping the option of expelling the Russian ambassador on the table.
But Senator Payne has reiterated that having Alexey Pavlovsky in the country allows the government to continue to communicate with the Russian government.
"That does not mean the government has excluded that option [of expelling the ambassador]," she said.
The Foreign Minister also said the international community was facing the "sensitive" issue of whether to allow Russia to take part in the G20 meeting later this year in Indonesia.
"We are dealing not just in relation to the G20 but multiple international and multilateral organisations and gatherings where this is a matter that we have to address.
"We'll work closely with other members of the G20 on this," Senator Payne said.
"But Russia's participation … is a serious issue and it's one the international community has to continue to examine."
Questions about Putin's attendance at G20
Prime Minister Scott Morrison has raised his and the federal government's concerns about Vladimir Putin attending a G20 meeting later this year.
The Russian President has signalled his intention to attend the meeting of the world's largest economies in Indonesia later this year, backed by China.
"[The invasion of Ukraine] is a violent and aggressive act that shatters the international rule of law, and the idea of sitting around a table with Vladimir Putin – who the United States are already in a position of calling out for war crimes in Ukraine, is for me, a step too far," Mr Morrison said.
"We want the Indonesian G20 to be a great success we want it to focus particularly on the challenges of our region."
Senator Payne said it was ultimately up to the G20 to decide if Mr Putin could attend the November meeting.
"These are very sensitive issues, we are dealing in not just in relation to the G20 but multiple international and multilateral organisation where this is a matter we have to address," she said.
ABC/Reuters
