US Attorney General Merrick Garland pledged during a surprise visit to Ukraine on Tuesday to help the Ukrainian authorities prosecute war crimes committed during the Russian invasion.

"I'm here to express the unwavering support of the United States for the people of Ukraine in the midst of the unprovoked and unjust Russian invasion," Garland told reporters after meeting Ukraine's Prosecutor General Iryna Venediktova at Krakovets on the Polish-Ukrainian border.

Garland announced the launch of a War Crimes Accountability Team headed by Eli Rosenbaum, a 36-year veteran of the Justice Department who previously led US efforts to identify and deport Nazi war criminals.

"America -- and the world -- has seen the many horrific images and read the heart-wrenching accounts of brutality and death that have resulted from Russia's unjust invasion of Ukraine," Garland said in a statement.

"There is no hiding place for war criminals. The US Justice Department will pursue every avenue of accountability for those who commit war crimes and other atrocities in Ukraine," he said.

Venediktova thanked Garland for his support, calling it "very important."

"We all understand that we have huge enemies," she said.

US Attorney General Merrick Garland is visiting Ukraine to discuss prosecution of individuals involved in war crimes
US Attorney General Merrick Garland is visiting Ukraine to discuss prosecution of individuals involved in war crimes AFP / ROBERTO SCHMIDT

Garland is stopping in Ukraine on his way to a US-EU justice and home affairs ministerial meeting this week in Paris.

Nearly four months after Russia invaded Ukraine, Kyiv says it has identified thousands of suspected war crimes cases.

Most notorious have been the allegations of wanton murder of scores of civilians in Bucha, just outside the Ukrainian capital.

US President Joe Biden has denounced the killing of Ukrainian civilians in Bucha as "war crimes."

"Civilians executed in cold blood, bodies dumped into mass graves, the sense of brutality and inhumanity left for all the world to see, unapologetically," Biden said in April.

"There's nothing less happening than major war crimes," he said. "Responsible nations have to come together to hold these perpetrators accountable."

The US State Department announced the creation of a new unit in May to research, document and publicize alleged war crimes by Russia in Ukraine.