GENEVA >> A U.N. investigator called Tuesday for Sri Lanka to investigate and file charges against soldiers shown in a graphic video shooting bound, blindfolded prisoners and abusing corpses in the final days of the 1983-2009 civil war.

The investigator, Christof Heyns, reviewed the 5-minute, 25-second video with a team of technical and forensics experts frame by frame to determine its authenticity, and told The Associated Press that the video suggests there is enough evidence to open a war-crimes case. Sri Lanka has claimed the video is fake.

In the video, several men lie on a muddy track, bound and motionless. The camera cuts and another man is shown being forced to sit upright by a soldier in camouflage carrying a rifle. Another soldier steps up behind the seated prisoner and shoots him in the back of the head, point blank. The prisoner slumps sideways as the camera pans across the road revealing nine bodies, most of them naked, with gunshot wounds clearly visible despite the grainy quality of the footage.

The uniformed men then force another blindfolded prisoner down into the dirt. A gunshot rings out and he, too, jerks and collapses. Later, the camera focuses on a young man, his skull blown open. Soldiers stand over the half-dressed corpse of a woman, gloating.

The Sri Lankan government says the video is staged, an attempt by pro-Tamil Tiger groups to undermine its hard-won victory in the country’s decades-old civil war.

“We have proven beyond any doubt that this is not authentic,” said Lakshman Hulugalla, director general of the government’s Media Center for National Security.

It has categorically rejected calls for an independent international probe into allegations of abuse carried out by Sri Lankan government forces in the north of the country in May 2009. Instead, the government says it has established a national panel to investigate. Human rights groups including Amnesty International say that isn’t enough.

Heyns, a South African law professor who is also the U.N.’s independent investigator on extrajudicial killings, told the AP the video shows “definitive war crimes.”

“There is a prima facie case and it should now go to the next level,” he said before screening the video for the first time to reporters in Geneva.

The United Nations estimates that between 80,000 and 100,000 people were killed in the 26-year war. This includes at least 7,000 ethnic Tamil civilians killed in the last five months of the conflict. Numerous U.N.-appointed officials have concluded that both sides committed atrocities.

A recent U.N. report said Sri Lankan government forces deliberately targeted civilians and hospitals, and blocked food and medicine for hundreds of thousands of civilians trapped in the war zone. It also accused the Tamil Tigers of recruiting child soldiers and using civilians as human shields.

The latest footage was obtained by Britain’s Channel 4, which has so far shown only brief excerpts and an earlier, shorter video of the same events. The station plans to screen the new video in its entirety next month. Human rights groups say it adds to existing evidence that crimes were committed that merit an independent international investigation and possible war-crimes prosecutions.

“It’s horrific, hellish scenes of what must surely be murder,” said Ben De Pear, head of foreign affairs for Channel 4 News. He said the station chose to broadcast the footage after the U.N. experts helped it conclude that it is genuine.