WASHINGTON (AP) — President Joe Biden on Monday called for a war crimes trial against Russia President Vladimir Putin and said he'd seek more sanctions after reported atrocities in Ukraine.

"You saw what happened in Bucha," Biden said. He added that Putin "is a war criminal."

Biden's comments to reporters came after Ukraine President Volodymyr Zelenskyy visited Bucha, one of the towns surrounding Kyiv where Ukrainian officials say the bodies of civilians have been found. Zelenskyy called the Russian actions "genocide" and called for the West to apply tougher sanctions against Russia.

"We do not believe that this is just a random accident, or the rogue act of a particular individual," said U.S. national security adviser Jake Sullivan of the images of bound civilians killed. He noted the U.S. had warned that Russia would seek to imprison or kill dissidents or others it viewed as threats to its attempted occupation of Ukraine. "We believe that this was part of the plan," he added.

Biden and U.S. officials, however, stopped short of calling the actions genocide.

"We have seen atrocities, we have seen war crimes, we have not yet seen a level of systematic deprivation of life of the Ukrainian people to rise to the level of genocide," Sullivan said.

The bodies of 410 civilians have been removed from Kyiv-area towns that were recently retaken from Russian forces, Ukraine's prosecutor-general, Iryna Venediktova, said. Associated Press journalists saw the bodies of at least 21 people in various spots around Bucha, northwest of the capital.

"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.

Biden lashed out at Putin as "brutal."

"What's happening in Bucha is outrageous and everyone sees it," Biden added.

Sullivan said Monday that Russia was shifting its focus in its war in Ukraine to the country's east and south, after experiencing a stronger-than-expected defense by Ukrainians supported by Western allies.

Sullivan said "the Russians have now realized that the West will not break" in its support of the Ukrainian government. But he warned that Russia was redoubling its offensive in other parts of the country after pulling many troops from around the capital of Kyiv.

White House officials said talks about ramping up new sanctions against Russia intensified after reports of alleged atrocities emerged. Biden said Monday that he would continue to add sanctions but did not detail what sectors the U.S. may target next. Sullivan said the additional sanctions would come this week.

After unveiling an avalanche of sanctions in the first weeks of the war, administration officials in recent days have put more focus on closing loopholes that Russia might try to use to avoid sanctions.

European Commission President Ursula von der Leyen tweeted Monday that the European Union will send investigators to Ukraine to help the local prosecutor general "document war crimes."

A Russian law enforcement agency says it has launched its own investigation into allegations that Ukrainian civilians were massacred in suburbs of Kyiv that were held by Russian troops, focusing on what it calls "false information" about Russian forces.

The Investigative Committee claims Ukrainian authorities made the allegations "with the aim of discrediting Russian troops" and that those involved should be investigated over possible breaches of a new Russian law banning what the government deems to be false information about its forces.

Biden noted that he faced pushback last month when he described Putin as a war criminal for the unfolding onslaught in Ukraine after hospitals and maternity wards were bombed. In his remarks on Monday, Biden made clear that label still applied.

"This guy is brutal and what's happening to Bucha is outrageous, and everyone's seen it," Biden said.

Investigations into Putin's actions had begun before the new allegations of atrocities outside Kyiv.

The U.S. and more than 40 other countries are working together to investigate possible violations and abuses, after the passage of a resolution by the United Nations Human Rights Council to establish a commission of inquiry. There is another probe by the International Criminal Court, an independent body based in the Netherlands. The U.S. Senate unanimously approved a resolution last month seeking investigations of Putin and elements of his government for war crimes over the invasion of Ukraine.

Meanwhile, Biden's chief envoy to the United Nations, Ambassador Linda Thomas-Greenfield, announced Monday that the U.S. plans to seek a suspension of Russia from its seat on the U.N.'s top human rights body in the wake of more indications Russian forces may have committed war crimes in Ukraine. That would require a decision by the U.N. General Assembly.

Russia and the other four permanent members of the U.N. Security Council – Britain, China, France and the United States – all currently have seats on the 47-member-state rights council, which is based in Geneva. The United States rejoined the council this year.

"My message to those 140 countries who have courageously stood together is simple: the images out of Bucha and devastation across Ukraine require us now to match our words with action," Thomas-Greenfield said. "We cannot let a Member State that is subverting every principle we hold dear to continue to sit on the UN Human Rights Council."

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Associated Press chief congressional correspondent Lisa Mascaro contributed reporting to this article.