Satellite photographs appear to rebut Russian assertions that dead bodies in civilian clothing found in Bucha had appeared after Russian forces retreated from the devastated Ukrainian town.
Moscow has claimed the scenes were faked and says it will present evidence to the UN Security Council.
It comes as Ukrainian President Volodymyr Zelenskyy, who visited Bucha on Monday, prepared to speak to the UN Security Council for the first time on Tuesday at a meeting certain to focus on what appear to be deliberate killings of civilians by Russian troops.
The satellite images, released by Maxar Technologies on April 4, show views of streets in Bucha, on the outskirts of Kyiv. Taken on March 31, they seem to show bodies lying in the streets, before Russian forces retreated from the devastated Ukrainian town.
They give the lie to Russian assertions that dead bodies in civilian clothing found in Bucha had appeared there afterwards.
"High-resolution Maxar satellite imagery collected over Bucha, Ukraine (northwest of Kyiv) verifies and corroborates recent social media videos and photos that reveal bodies lying in the streets and left out in the open for weeks," Maxar Technologies said on Monday in a statement.
The Russian government and pro-Kremlin media have claimed that Russian troops left Bucha on 30 March, and that the bodies were first documented only on 3 April.
But on 1 April, Russian media outlet Zvezda TV reported that Russian marines were still carrying out operations in areas including Bucha.
The Irpin-Bucha-Hostomel Telegram channel published video showing bodies in the streets, also on 1 April.
The same day, a Kyiv regional authority report listed the town as among the most dangerous areas due to the presence of Russian forces.
The BBC reported on 1 April that at least 20 bodies were seen lying in the street as the Ukrainian military entered the town. A Ukrainian military report on 31 March said Bucha was still under Russian control.
Independent journalists have seen, filmed and photographed the bodies found in Bucha and elsewhere, some in areas occupied by Russian forces only hours before. The investigative site Bellingcat and the US think tank the Atlantic Council have published detailed fact-checks contesting the Russian claims.
On Monday Associated Press journalists in Bucha counted dozens of corpses in civilian clothes and apparently without weapons, many shot at close range, and some with their hands bound or their flesh burned.
Kremlin spokesperson Dmitry Peskov said on Monday that the images contained “signs of video forgery and various fakes”. Russian Foreign Minister Sergey Lavrov dismissed the scenes outside Kyiv as a “stage-managed anti-Russian provocation,” prompting one Ukrainian MP to accuse him of lying.
"Just for that he has to be brought to responsibility in front of a criminal court because these are lies, and these are absolutely unacceptable lies about human lives," Ukrainian lawmaker Lesia Vasylenko told BBC radio.
"Who is taking those pictures and who is making those videos? The Ukrainian military, who is there on site, Ukrainian territorial defence who is also on site, and also international media... British, American, French, they are all there on site with their cameras and they can see what is happening, and it's impossible to stage these kinds of crimes."
She went on to call for the United Nations and its member states to act.
"We are talking about the crime of aggression, we are talking about the crime of genocide, which is being committed in the middle of Europe in the middle of the 21st century, and everybody is standing on the sidelines, not performing their responsibilities... and just watching all these crimes in Ukraine as if it was a Netflix documentary or TV series."
"Russian aggression is on the rise... because Putin is not being stopped," she said.