Ukraine has identified several thousand suspected war crimes in the eastern Donbas region where Russian forces are pressing their offensive, Kyiv's chief prosecutor said on Tuesday.

The cases in the industrial region are among some 15,000 across Ukraine since Russian forces attacked on February 24, prosecutor general Iryna Venediktova said.

"Of course we started a few thousand cases about what we see in Donbas," Venediktova told a news conference in The Hague as she met international counterparts.

"If we speak about war crimes, it's about possible transfer of people, we started several cases about possible transfer of children, adult people to different parts of the Russian Federation," she said.

"Then, of course, we can speak about torturing people, killing civilians and destroying civilian infrastructure."

Ukrainian authorities did not have access to Russian-held areas of Donbas, but they were interviewing evacuees and prisoners of war, Venediktova told the press conference at the headquarters of EU judicial agency Eurojust.

In total, Ukraine had identified 15,000 war crimes cases since the Russian offensive with 200 to 300 more coming in every day, she added.

Ukraine had identified 600 suspects for the "anchor" crime of aggression, including "high level of top military, politicians and propaganda agents of Russian Federation", the prosecutor general said.

Nearly 80 suspects had been identified for alleged war crimes that had actually taken place on Ukrainian soil, she added.

Two Russian soldiers were jailed for 11 and a half years by a Ukrainian court on Tuesday for shelling civilian areas, while another was jailed for life earlier this month for murdering a civilian.

Three more European countries – Latvia, Estonia and Slovakia – meanwhile joined an international investigation team probing war crimes in Ukraine on Tuesday.

Prosecutors from Poland, Lithuania and from the Hague-based International Criminal Court are already part of the team.

"Today is a momentous day that the (team) has three new members," ICC prosecutor Karim Khan said at the news conference alongside the Ukrainian prosecutor.

The ICC was "hopefully" going to open a field office in Kyiv in the next few weeks to have a more permanent base for its investigation in Ukraine, Khan added.

"We can't fly in and fly out," said Khan.

The ICC earlier this month dispatched the largest team of investigators in the court's 20-year history to probe suspected war crimes and crimes against humanity in Ukraine.

Ukraine's Venediktova said she hoped her country would handle "95 percent" of cases but that some larger or more difficult ones could be dealt with by the ICC.

Russia's assault and the subsequent discovery of hundreds of killings in places such as the Kyiv suburb of Bucha have prompted unprecedented international investigative efforts.

"Never in the history of armed conflict has the legal community responded with such determination," Eurojust President Ladislav Hamran said. (AFP)