United Nations Secretary-General Antonio Guterres said on Sunday he was “deeply shocked” by the footage of civilians killed in the Ukrainian city of Bucha and called for an independent investigation that “leads to effective accountability”.

Guterres posted his comments on Twitter a day after witnesses and officials said Russian troops had killed nearly 300 civilians as they retreated from the town of Bucha, near Kyiv.

“I was deeply shocked by the images of civilians killed in the Ukrainian city of Bucha,” Guterres said, joining other Western officials who voiced his anger.

“It is essential that an independent investigation leads to effective accountability for these actions,” he said.

Russia’s Defense Ministry denied that Russian forces had killed civilians in Bucha, saying the videos and photos of the bodies were “another provocation” by the Ukrainian government.