(WASHINGTON) — The killings of Ukrainian civilians committed by Russian forces in Ukraine is a war crime, President Joe Biden said Monday — repeating his accusation that Russian President Vladimir Putin is a “war criminal” who needs to be held “accountable.”

Ukrainian President Volodymyr Zelenskyy accused Russia of “genocide” on Sunday after hundreds of Ukrainian civilians were found killed in Bucha, a suburb of the capital Kyiv that was retaken by Ukrainian forces. Some of the civilians were buried in mass graves, others found dead in the street with their hands tied behind their backs.

“These are war crimes, and they will be recognized by the world as genocide. You are here today and can see what happened. We know of thousands of people killed and tortured, with severed limbs, raped women, murdered children. I think it is more than — this is a genocide,” Zelenskyy told reporters in Bucha Monday.

The U.S. has stopped short of using the term “genocide” because of its strict legal definition and the heavy implications it carries. Asked whether the latest reported atrocities are genocide, Biden told reporters, “No, I think it is a war crime.”

He called again for an investigation and trial, even seeming to suggest that Putin himself should face a courtroom.

“We have to continue to provide Ukraine with the weapons they need to continue the fight, and we have to gather all the detail so this can be an actual — have a war crimes trial,” Biden said.

“This guy is brutal and what’s happening with Bucha is outrageous, and everyone’s seeing it,” he added.

While stopping short of labeling it “genocide,” Biden’s call for for a possible war crimes trial raises the pressure on the international community’s response to Russia’s war, which has killed thousands and displaced more than 10 million people in less than six weeks.

Biden said he would seek more sanctions against Putin and his government over the atrocities in Bucha, although it’s unclear if more economic pressure will do anything to bring an end to Putin’s campaign, even as it has shifted away from the Kyiv area to the south and east.

The Kremlin has suggested that the scenes, reported publicly by eye witnesses, reporters, and Ukrainian government officials, were fabricated — a tactic used repeatedly by Russian officials.

Last month, the State Department announced it had made a legal assessment that Russian forces were committing war crimes in Ukraine, including targeting civilians and civilian infrastructure and indiscriminately firing on civilian areas. That assessment was based on public reporting and U.S. intelligence, including intercepted communications between Russian forces, according to U.S. Ambassador-at-Large for Global Criminal Justice Beth Van Schaack.

That could implicate Putin himself, according to Van Schaack, who told reporters it depended on what jurisdiction was hearing cases. Her office at the State Department has continued to document and analyze evidence in preparation for trials.

But while her office also assists in genocide determinations, U.S. officials have so far avoided using the term.

Genocide is an attempt “to destroy, in whole or in part, a national, ethnic, racial, or religious group,” according to the Convention on the Prevention and Punishment of the Crime of Genocide, the 1948 treaty that banned it.

It can involve acts of killing or harm, as well as preventing births, forcibly transferring children, or imposing dire conditions that are “calculated to bring about its physical destruction,” per the treaty.

There are several international investigations underway right now into potential war crimes in Ukraine. The International Criminal Court, which conducts individual prosecutions, launched an investigation in early March, while the United Nations Human Rights Council voted to create a panel of experts to investigate, finally naming its members last week.

While the State Department’s work will support those investigations, its genocide determinations can take years to complete.

Last month, Secretary of State Antony Blinken announced he had determined that Myanmar’s military had committed genocide against the Rohingya — nearly five years after the Muslim ethnic minority faced a campaign of terror that killed thousands and displaced nearly one million to neighboring Bangladesh.

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