(CNN) US Ambassador to the United Nations Linda Thomas-Greenfield said Thursday that actions committed by Russia against the Ukrainian people constitute war crimes, marking the first time a senior US official has directly accused Moscow of war crimes since last month's attack on Ukraine began.
"They constitute war crimes; there are attacks on civilians that cannot be justified by any -- in any way whatsoever," she said in an interview with BBC "Newshour" on Thursday morning.
Other Biden administration officials have not gone as far as to declare outright that Russia has committed war crimes -- violations of international laws of armed conflict -- and instead have pointed to "credible reports" that such crimes have been carried out and their support for investigations into Moscow's actions.
Vice President Kamala Harris on Thursday referenced "atrocities" committed by the Russians and said that the UN should investigate the allegations of Russian war crimes.
Later on Thursday State Department spokesperson Ned Price said the US has "seen very credible reports" of Russian actions that would constitute war crimes, echoing comments made by Secretary of State Antony Blinken on Sunday.
Thomas-Greenfield said in the interview with the BBC that the question of whether Russia is guilty of war crimes is the one "we're being asked every day, and we're working with others in the international community to document the crimes that Russia is committing against the Ukrainian people."
"I still see images of a women being rolled out of a hospital, pregnant, bleeding, people screaming, children crying. It is just unconscionable. And we call on Russia to change course. They have to end this conflict, and they have to stop the fighting, and they have to return to diplomacy. And we have made clear our strong support for Ukrainians' call for this to stop," she added.
Thomas-Greenfield said she couldn't predict how the war crimes would be prosecuted, but "what is important is that we collect the evidence and have the evidence ready and available to be used."
The ambassador also indicated that the US is supportive of the International Criminal Court (ICC) probe of Russia's actions in Ukraine, despite the US not being a member of the ICC and criticizing other ICC investigations.
"We've always been supportive of the Criminal Court taking actions when actions are required," she said.
Speaking at a State Department briefing later Thursday, Price also welcomed the ICC investigation, noting its focus on the preservation of evidence -- a key factor in making an official determination that war crimes have been committed.
"We want to see evidence preserved. We are and will be in the process of marrying reports with evidence from the ground, and if we determine, if the international community determines that war crimes have been committed, that atrocities have been committed, that human rights abuses have been committed, we absolutely will hold the perpetrators accountable, whether they sit in Moscow, or whether they're commanders on the ground in Ukraine," Price said.
"The fact is that we've seen very credible reports of deliberate attacks on civilians, which would, under the Geneva Conventions, constitute a war crime," he said, citing attacks on the hospital in Mariupol and strikes on schools, hospitals, buses, cars and ambulances.
Harris, who spoke at a news conference alongside Polish President Andrzej Duda in Warsaw on Thursday morning, said that Russia's attacks in Ukraine amounted to "atrocities of unimaginable proportions." But, she stopped short of calling Russia's actions war crimes. "We are also very clear that any intentional attack on innocent civilians is a violation," Harris said.
"The UN has set up a process by which there will be a review and investigations, and we will of course participate as appropriate and necessary," she added. "I have no question the eyes of the world are on this war and what Russia has done in terms of this aggression and these atrocities."
Duda was more direct, calling war crimes "obvious" in Ukraine and saying refugees coming to his country have evidence of it on their phones.
A senior administration official said that Harris' comments were in line with the administration's position that the deliberate targeting of civilians would be defined as a war crime and should be investigated, saying she was referring to an investigation through the UN Commission of Inquiry.
On Sunday, Blinken said that the US is looking into "credible reports of deliberate attacks on civilians, which would constitute a war crime," but had not declared that the US had made the assessment that Moscow was guilty of war crimes.
"What we're doing right now is documenting all of this, putting it all together, looking at it, and making sure that as people and the appropriate organizations and institutions investigate whether war crimes have been or are being committed, that we can support whatever they're doing," Blinken said on CNN's "State of the Union." "So right now we're looking at these reports. They're very credible. And we're documenting everything."