A U.N. human rights expert says new footage from the final days of the Sri Lankan civil war in 2009 is authentic and proves war crimes took place.

The U.N.'s independent investigator on extrajudicial killings says the five-minute video obtained by Britain's Channel 4 shows uniformed men executing unarmed women and men.

Sri Lanka's government has claimed the footage and an earlier, shorter video are faked.

But the U.N. investigator, South African law professor Christof Heyns, says he reviewed the footage with technical and forensic experts and concludes it "is authentic and the events reflected in the video footage occurred as depicted."

Heyns' report Monday to the U.N. Human Rights Council is expected to dominate the Geneva body's three-week meeting.