Russia waged a deliberate campaign to commit atrocities in the Ukrainian town of Bucha, and the United States is supporting the efforts of the Ukrainian authorities in their investigation of these acts, U.S. Secretary of State Antony Blinken said on Tuesday.

"What we've seen in Bucha is not the random act of a rogue unit," Blinken told reporters before departing for Brussels for a NATO foreign ministers' meeting.

"It's a deliberate campaign to kill, to torture, to rape, to commit atrocities," he said.

Also on Tuesday NATO Secretary General Jens Stoltenberg described the civilian deaths around Kyiv as "unbearable brutality that Europe has not witnessed in many decades."

Russia, which says it launched a "special military operation" in Ukraine on Feb. 24 to demilitarize and "denazify" its neighbour, denies targeting civilians and said the deaths were a "monstrous forgery" staged by the West to discredit it. Satellite images and analysis of video in Bucha have undermined that claim.