A U.S. official on Tuesday dismissed as ridiculous claims by Russia that Georgia committed genocide during fighting this month in two breakaway Georgian regions.

Deputy Assistant Secretary of State Matthew Bryza also demanded Russian action to end human rights violations in areas of Georgia occupied by its troops.

Russia and Georgia, an ally of the United States, have been exchanging accusations of atrocities in the conflict that has led to a major rift between Russia and Western countries.

Georgia launched a heavy artillery barrage Aug. 7 on South Ossetia, a separatist Georgian province with close ties to Russia. Last week, Russian troops drove Georgian forces out of South Ossetia, and conflict also broke out in a second Russian-backed separatist region, Abkhazia.

Russian prosecutors have opened a genocide probe into Georgian treatment of South Ossetians. Georgia sued Russia in international court, alleging murder, rape and mass expulsions of Georgians in both provinces.

Bryza, speaking to reporters, called reports of human rights violations, including murder and rape, credible in areas of Georgia now controlled by Russia, but said they appeared to be committed by Russian-backed irregular militias rather than the Russian military.

"As peacekeepers, or as human beings, members of the Russian military are responsible for making sure that the territory that they now occupy is free from these ravages against the local population," Bryza said. He said that in South Ossetia, local militias have in the past been commanded by Russia.

He said there was no credible evidence that Georgia had tried to wipe out civilian populations in the two regions.

"The claims of genocide or of ending the South Ossetian and Abkhaz people, they are downright false and ridiculous," Bryza said.