Anatoly Fedoruk, Bucha’s mayor, said the corpses of men, women and children had been found littered across the town’s streets on Saturday.
Accounts of civilian killings have been reported by numerous witnesses in areas recently abandoned by Russian forces, which withdrew from several dozen settlements around Kyiv this week.
Videos from the ground show at least 20 bodies – mainly men in civilian clothes – lying in a single street. Some appeared to have their hands tied behind their backs.
“All these people were shot, killed, in the back of the head,” Mr Fedoruk said.
Bucha is a town in Kyiv Oblast that, before the war, was home to around 37,000 people. Analysts fear that further mass graves will be discovered as more areas are liberated.