Ukraine accused Russian forces of a massacre of civilians on the outskirts of Kyiv after discovering bodies left strewn across streets in the wake of a pullback by Kremlin troops.
European leaders vowed to support efforts to prosecute possible war crimes, as Human Rights Watch said it had documented criminal abuses by Russian soldiers, including repeated rape and summary executions.
"The cases we documented amount to unspeakable, deliberate cruelty and violence against Ukrainian civilians," said the organisation's regional director Hugh Williamson.
As Ukrainian forces reclaimed the town of Bucha near Kyiv over the weekend from Russian forces, they found streets littered with dead people in civilian clothing, some with their hands tied behind their backs, according to photographic and video footage.
A Russian commander told locals in Bucha, “we are here to cleanse you” as his soldiers shot a kneeling young man in the back of the head, a woman who survived told Human Rights Watch.
The local mayor told Agence France-Presse that 260 people had been buried and that families still lay dead in their cars, killed as they tried to escape.
Among the bodies recovered as Russian troops withdrew from the Kyiv region to consolidate their forces in eastern Ukraine was that of missing photographer Maksim Levin, and local village leader Olha Sukhenko who was executed by Russian soldiers after they abducted her and her family, the Kyiv government said.
Britain's ambassador to Ukraine Melinda Simmons said that reported atrocities made it "already clear" that Russia was using rape as a "weapon of war".
Russia denied targeting local civilians and a diplomat described footage of the dead people in Bucha as a “hoax”. In a statement, the Russian defence ministry said the incident was a “provocation” and a “staged performance” by the Kyiv government.
Western leaders expressed outrage and vowed to support the investigation of possible war crimes by the International Criminal Court.
UN secretary general António Guterres yesterday called for an independent investigation into the killing of civilians in Bucha.
Minister for Foreign Affairs Simon Coveney said there can be “no impunity” for atrocities committed in Ukraine by Russian forces.
"The Russian authorities will have to answer for these crimes," wrote French President Emmanuel Macron.
Ukraine's foreign minister Dmytro Kuleba warned that the situation in the bombarded and besieged city of Mariupol was likely to be worse than Bucha, and called for more weapons to push the Russian army out of Ukraine's east, warning that those who denied his country help would "share responsibility" for civilian deaths.
Meanwhile, it emerged that Russian ambassador Yuriy Filatov is to be invited to attend Ukrainian president Volodymyr Zelenskiy's address to the joint houses of the Oireachtas.
Mr Zelenskiy is to address the Dáil and Seanad on Wednesday. While he said he would not comment on any particular nation, Ceann Comhairle Seán Ó Fearghaíl said that all accredited ambassadors to Ireland would be invited to sit in the public gallery during the event.