Ukrainian forces have buried some 300 people in a mass grave in a suburb of the capital Kyiv, a local official has reported.

"In Bucha, we have already buried 280 people in mass graves," Mayor Anatoly Fedoruk told AFP on Saturday. "All these people were shot, killed, in the back of the head."

In a later report, Fedoruk told Reuters that more than 300 residents had been killed.

The mayor blamed Russia's military for the killings in his town, which was only recently retaken by Ukrainian forces.

Russia has not responded to the accusation, but has previously said that its "special military operation" only destroys Ukrainian military targets and does not target civilians.