Kamala Harris Embraces Efforts to Investigate Russia for Possible War Crimes in Ukraine

“The U.N. has set up a process by which there will be a review and investigations, and we will of course participate as appropriate and necessary,” Ms. Harris told reporters in Warsaw. “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.”

War crimes, broadly defined, include willfully killing or causing suffering, widespread destruction and seizing of property, deliberately targeting civilian populations, and other serious violations of laws applicable in armed conflict. The International Criminal Court also prosecutes three other offenses: crimes against humanity, genocide and the crime of aggression.

Charging Russian President

Vladimir Putin

or his commanders with war crimes is a complex legal issue, compounded in part by the fact that Russia, along with the U.S. and China, isn’t a party to the ICC.

The U.S. ambassador to the United Nations,

Linda Thomas-Greenfield,

on Thursday told the BBC that Russia’s actions “constitute war crimes.” While she couldn’t predict how Russia’s actions will be prosecuted, she said, “What is important is that we collect the evidence and have the evidence ready and available to be used.”

“There are attacks on civilians that cannot be justified by any—in any way whatsoever,” she said.

Both Ms. Thomas-Greenfield and Ms. Harris cited images of pregnant women being evacuated from a maternity hospital in Mariupol hit Wednesday by the Russian military.

The ICC last week opened an investigation into possible war crimes in Ukraine, an early step in a process that potentially could lead to Mr. Putin and other Kremlin leaders being charged at The Hague. Kremlin spokesman

Dmitry Peskov

said Russia “categorically rejects” the ICC investigation.

The U.S. State Department has said it would use every tool available to hold Russia to account for violations of human rights or international law. Still, Washington and Moscow aren’t part of the ICC agreement, and Russia’s permanent seat on the U.N. Security Council would allow it to block a referral from there.

Unless there’s a change of power at the Kremlin, Russian President Vladimir Putin and the country’s military officers are unlikely to go on trial for any such possible crimes, experts say.

Separately, the International Court of Justice held a hearing in recent days on Ukraine’s claims against Russia under the Genocide Convention. Moscow boycotted the hearing.

Ukraine sought the proceedings at the world court, a branch of the U.N., “to establish that Russia has no lawful basis to take action in and against Ukraine for the purpose of preventing and punishing any purported genocide,” after Moscow accused Kyiv of killing civilians in the Russia-backed separatist regions of Luhansk and Donetsk. Kyiv also accused Russia of “planning acts of genocide in Ukraine” and of intentionally killing Ukrainians.

Russia is facing some pressure at the U.N. Human Rights Council, which on Friday voted to establish an independent international inquiry into alleged violations in Ukraine. The U.S., which rejoined the council under the Biden administration, voted in favor of the inquiry along with 31 other countries, while Russia and Eritrea voted against it and 13 countries abstained.

In recent days, Moscow has accused the U.S. of working with Ukraine on chemical weapons and dangerous biological experiments with a military purpose. Western officials say Russia may be laying the groundwork for using chemical weapons after its invasion of Ukraine hit stiff resistance.

“There’s a sentiment growing among Putin and his inner circle that they will need to escalate the types of weapons that they’re dealing with,” said Sophia Gaston, director of the British Foreign Policy Group, a London think-tank. “We know from the way Russia behaved in Syria that they’re comfortable engaging in unconventional types of warfare and weaponry that transgresses international norms.”

While in Poland, Ms. Harris also announced humanitarian aid for some of the 1.5 million Ukrainians who have fled to Poland. She said the U.S. would offer $50 million in assistance through the World Food Program to help Poland manage what has become Europe’s biggest refugee crisis since World War II.

Ms. Harris also said that the U.S. is discussing with Poland and other allies the effectiveness of sanctions and said that Russia needs to suffer severe consequences for its invasion of Ukraine.

Poland, America’s most important military ally in the European Union’s east, is pushing the U.S. to do more. During his meeting with the vice president, Mr. Duda said he had asked the U.S. to expedite visas for Ukrainians in Poland who want to join family in the U.S. He also asked for more sanctions on Russia.

“We cannot accept more military operations which carry the features of a genocide,” Mr. Duda said, mentioning the attack on a maternity ward in Mariupol. “This is an act of barbarity, with features of a genocide, aimed at the elimination of a nation.”

—Jess Bravin contributed to this article.