JDS says the video had been taken in January 2009 using a mobile phone

The Sri Lankan High Commissioner to London, Nihal Jayasinghe, said the identity of the executioners - or their naked victims - could not be known for certain.

"How can one say looking at the video that these are Sri Lankan soldiers executing Tamil people? I just can't imagine how an expert can ever say those people are Sri Lankan soldiers and the people who are naked are Tamil Tigers," he told the BBC.

Earlier a United Nations investigator said independent experts were convinced the video was genuine.

Philip Alston, the Special Rapporteur on extrajudicial, summary or arbitrary executions said three experts in forensic pathology have concluded that the video is authentic.

He has called for a war crimes investigations into the incident.

"The conclusion I have reached is the following; In light of the persistent flow of other allegations of extra judicial executions committed by both sides during the closing phases of the war, against the LTTE, I call for an independent inquiry to be established to carry out an impartial investigation into war crimes and other grave violations of international humanitarian and human rights law, allegedly committed in Sri Lanka," he told the BBC.

Last month, a Sri Lankan newspaper printed allegations attributed to a former army commander, Gen Sarath Fonseka that the government had ordered rebels to be killed and not allowed to surrender.