Ukraine has identified more than 600 Russian war crime suspects since the start of the invasion, Kyiv's top prosecutor has said.
The list of suspects includes "top military, politicians and propaganda agents of Russia”, prosecutor general Iryna Venediktova told a news conference in The Hague on Tuesday.
She added Ukraine has started prosecuting around 80 of them.
Venediktova said Estonia, Latvia and Slovakia had decided to join an international investigation team, which already includes Lithuania and Poland, to look at suspected war crimes in Ukraine.
Moscow denies committing war crimes or targeting civilians during a conflict which began in February that has killed thousands, devastated many cities and towns and forced five million people to flee abroad.
Kyiv has accused Russia of atrocities and brutality against civilians during the invasion and said it had identified more than 10,000 possible war crimes.
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Venediktova and her team have in the last few weeks been evaluating sites where atrocities have allegedly taken place, including where Russian troops have withdrawn.
On 12 April, she visited Bucha, near Kyiv, where French forensic experts had arrived to help Ukraine authorities establish what happened in the town where hundreds of bodies were discovered.
Bucha’s mayor said dozens were the victims of extra-judicial killings by Russian troops.
Lyudmyla Denisova, the Ukrainian parliament's human rights commissioner, added 25 women and girls, aged from 14 to 24, had called a helpline reporting they had been raped in Bucha.
Venediktova's team is working with the International Criminal Court (ICC), which launched its investigation into possible war crimes in Ukraine in early March.
ICC prosecutor Karim Khan's office has deployed a team of 42 investigators, forensic experts, and support personnel to Ukraine.
Venediktova said international support was vital to Ukraine's efforts to investigate all possible war crimes.
She said: "We should collect and protect everything in the right way. It should be acceptable evidence in any court."
Meanwhile, a Ukrainian court has sentenced two captured Russian soldiers to 11-and-a-half years in jail for shelling a town in eastern Ukraine, the second war crimes verdict since the start of Russia's invasion in February.
Alexander Bobikin and Alexander Ivanov, who listened to the verdict standing in a reinforced glass box at the Kotelevska district court in central Ukraine, pleaded guilty last week.
On 23 May, a Ukrainian court sentenced 21-year-old Russian soldier Vadim Shishimarin to life in prison for killing an unarmed civilian, 62, after he pleaded guilty.
Russia has accused Kyiv of genocide against Russian speakers, which Kyiv strongly denies.
Moscow has also opened criminal cases into Ukrainian servicemen's alleged torture of their Russian counterparts.
Russia calls its actions in Ukraine a "special military operation" to disarm and "denazify" its neighbour.
Kyiv and the West consider this a pretext for an unprovoked invasion.