Investigators from almost a dozen countries combed bombed-out towns and freshly dug graves in Ukraine on Wednesday for evidence of war crimes, and a wide-ranging investigation by an international security organization detailed what it said were “clear patterns” of human rights violations by Russian forces.
Some of the atrocities may constitute war crimes, said investigators from the Organization for Security and Cooperation in Europe, who examined myriad reports of rapes, abductions and attacks on civilian targets, as well as the use of banned munitions.
On Wednesday, civilians were still bearing much of the brunt of the seven-week-old invasion as Russian forces, massing for an assault in the east, bombarded Ukraine’s second-largest city, Kharkiv, striking an apartment building.
In an hourlong phone call with Volodymyr Zelensky, Ukraine’s leader, President Biden said the United States, already a major provider of defensive armaments to Ukraine, would send an additional $800 million in military and other security aid. The package will include “new capabilities tailored to the wider assault we expect Russia to launch in eastern Ukraine,” Mr. Biden said in a statement.
American officials also said Wednesday that the United States, in helping Ukraine prepare for such an assault, had increased the flow of intelligence to Ukraine’s government about Russian forces in eastern Ukraine and the Crimean Peninsula, which Russia seized from Ukraine eight years ago.
War crimes claims are famously difficult to investigate, and still harder to prosecute. It’s rare for national leaders to be charged, and even rarer for them to end up in the defendant’s chair.
But the war in Ukraine may prove different, some experts say, and momentum has been building to hold the Kremlin leadership responsible.
An International Criminal Court investigation into possible war crimes has been underway since last month, and a number of countries have been looking at ways for the United Nations to help create a special court that could prosecute Russia for what is known as the crime of aggression. Other possibilities include trying Russians in the courts of other nations under the principle of universal jurisdiction, the legal concept that some crimes are so egregious they can be prosecuted anywhere.
Part of the motivation for accountability is the revulsion in Europe and much of the world over the behavior of President Vladimir V. Putin’s forces, including reported executions of bound civilians and other atrocities.
War crimes experts also point to technological advances in forensic tools like facial identification software not available to those looking into earlier conflicts, and the sheer number of investigators on the ground in Ukraine — crucially, with the government’s blessing. A dozen French investigators joined the inquiries this week.
“There will be prosecutions, and probably all over the world,” said Leila Sadat, an international law professor at Washington University in St. Louis, and a longtime adviser to the chief prosecutor of the International Criminal Court on crimes against humanity. “Ukraine is actually crawling with war crimes investigators right now.”
Still, experts warned that the process would be slow, and that any early indictments would most likely be against lower-ranking Russian officials and armed-service members. Russia, which has described the accusations as fictional or unfounded, is not expected to cooperate in any prosecution.
The report released Wednesday by the Organization for Security and Cooperation in Europe, a 57-member organization based in Vienna that includes Russia, Ukraine and the United States, is one of the first in-depth studies of human rights abuses during Russia’s offensive against Ukraine.
Investigators looked at some of the most notorious attacks and other violent acts of the war, including Russia’s bombings of a theater and a maternity hospital in the besieged city of Mariupol, both depicted in the report as apparent war crimes.
They also pored through accounts of other horrific, if less visible, acts of violence. “There are allegations of rapes, including gang rapes, committed by Russian soldiers in many other regions in Ukraine,” they wrote.
But often, they were stymied.
Russia declined to cooperate with the three-person team of investigators, making it “impossible for the mission to take account of the Russian position on all pertinent incidents,” the report said.
Investigators found that Ukrainian forces, too, had been guilty of some abuses, particularly in the treatment of prisoners of war. “The violations committed by the Russian Federation, however, are by far larger in nature and scale,” their report said.
Michael Carpenter, the American ambassador to the O.S.C.E., said the report “documents the catalog of inhumanity perpetrated by Russia’s forces in Ukraine.” The European Union issued a similarly positive appraisal.
“This war is not only fought on the ground,” the bloc said in a statement. “It is clear that the Kremlin is also waging a shameful disinformation campaign in order to hide the facts of Russia’s brutal attacks on civilians in Ukraine. Reliable information and collection of facts have therefore never been as important as today.”
The Kremlin’s own mission to the O.S.C.E. dismissed the findings as “unfounded propaganda.”
On Tuesday, even as the Ukrainian authorities were unearthing bodies in full view of international journalists and other observers, Mr. Putin called the atrocities a “fake” that had been elaborately staged by the West.
On Wednesday, standing near the site of two mass graves, Ukraine’s prosecutor general, Iryna Venediktova, said there was an obligation both to uncover the facts and to do so in a transparent way to combat Russian disinformation.
“When you see dead bodies here, from the other side, from the Russian Federation, they say it is all fake, all this is our theater,” Ms. Venediktova said.
Ukrainian prosecutors and the newly arrived team of French experts exhumed bodies this week from mass graves in Bucha, a Kyiv suburb, where hundreds of civilians were killed during the brief Russian occupation of the area. The French government said that its team included ballistics and explosives experts and that it had the ability to do rapid DNA tests.
Evidence from the French investigation and others involving several different countries will be channeled to the International Criminal Court, which started looking into possible war crimes a week after the Feb. 24 invasion. Although Ukraine is not part of the agreement that created the court two decades ago, it has granted the court authority to investigate and prosecute in this conflict.
Investigators say they are intent on showing the world the reality of the war.
“They can see everything. They can see the situation here: real graves, real dead bodies, real bomb attacks,” Ms. Venediktova said. “That’s why for us this moment is very important.”
The O.S.C.E. report described a range of subterfuge by Russian forces, including the use of Red Cross emblems, white flags, Ukrainian flags and civilian clothes. And the organization’s investigators expressed concern that both sides might be holding more prisoners than disclosed.
On Wednesday, President Zelensky spoke directly about one of them: Viktor Medvedchuk, a Ukrainian politician and ally of Mr. Putin’s who was detained this week. Mr. Zelensky proposed exchanging him for Ukrainians held captive by Russian forces.
Even as agreement grew among many world leaders that war crimes charges were warranted, there was some disagreement over how to characterize Russia’s actions. Some leaders, among them Mr. Biden, have begun to use the term “genocide” — an escalation of his rhetoric. On Wednesday, France’s president, Emmanuel Macron, dissented.
“What is happening is madness, it’s a brutality that’s unheard-of,” Mr. Macron said. But, he said, “Genocide has a meaning. The Ukrainian people and the Russian people are brethren people.”
“I’m not sure that an escalation of words serves the cause,” he said.
The war crimes report came amid signs that Russia’s invasion may have backfired in at least one respect. Mr. Putin has long objected to NATO’s expansion eastward into the onetime domains of the Soviet Union, describing it as a fundamental threat to Russia. But on Wednesday, two militarily nonaligned nations, Finland and Sweden, said they were seriously considering joining the alliance.
Legal experts did not rule out the possibility, some day, of an indictment of Mr. Putin, who has already been castigated as a war criminal by some Western leaders. And were Mr. Putin to be criminally charged by a court outside Russia, it would likely mean he would have to restrict his international travel in order to minimize the risk of possible arrest were he to venture beyond Russia’s borders.
David Crane, a legal scholar at Syracuse University who was the chief prosecutor for the Special Court for Sierra Leone, an international war crimes tribunal that convicted the former president of Liberia, Charles G. Taylor, said he was confident that the International Criminal Court or some other judicial body would find legal grounds to charge the Russian president.
And even if Mr. Putin is never arrested and remains the leader of Russia, he said, the legal and diplomatic consequences of a war crimes indictment would severely undermine his credibility.
It would be as if “there’s like an ash mark on his forehead,” Mr. Crane said. “There’s no good options for him.”
Marc Santora reported from Warsaw, Erika Solomon from Berlin and Carlotta Gall from Bucha, Ukraine. Reporting was contributed by Jane Arraf from Lviv, Ukraine; Aurelien Breeden from Paris; Cora Engelbrecht from Krakow, Poland; Farnaz Fassihi from New York; Eric Nagourney from Los Angeles; and Rick Gladstone from Eastham, Mass.