New video evidence of the alleged executions of bound prisoners in Sri Lanka has emerged and is to be broadcast in full in a documentary, as pressure builds for an international investigation.

Fresh footage reveals new evidence of Sri Lanka executions

Footage has emerged purporting to show devastating new evidence of the summary execution of Tamil prisoners by government soldiers in Sri Lanka.

Readers are advised that they may find some of the detail in this article distressing.

In a separate incident to the one Channel 4 News broadcast last year, never before seen mobile phone footage has emerged, which experts say appears to depict genuine executions of people bound and blindfolded.

The raw footage and pictures will be broadcast in full for the first time in the Channel 4 documentary Sri Lanka's Killing Fields at 11:05 pm on Monday night.

The footage, allegedly captured on a mobile phone by a soldier as a trophy video, shows three people, including one woman, dressed in civilian clothes and kneeing on the floor in a wooded area.

Their eyes are covered and their hands appear to be tied behind their backs.

Missed the film?

A group of soldiers carrying guns look down on the group as one man, who appears to be in charge, goads others into shooting the prisoners.

"Is there no one with the balls to kill a terrorist?" he says, while calling another a "wimp" for not firing his gun.

"This bugger has a weapon and still seems scared of a terrorist," he says.

The soldiers are then instructed to raise their weapons and aim "directly at the head".

As gun shots ring out, two prisoners fall on their sides, while the other falls on his face, his blood covering the ground.

Metadata encoded within the video indicates it was recorded on 15 May 2009, amid a final push by government forces to drive out Tamil fighters in the last few days of the bloody civil war.

During this period up to 40,000 Sri Lankan civilians are believed to have died.

In a second new video, a man tied to a coconut tree is again filmed by soldiers on a mobile phone. Visibly in shock, shirtless and with blood covering his chest, he shifts his body as a circle of soldiers surround him.

In a series of photographs passed to Channel 4 of the same incident, the prisoner is threatened with a knife while still tied to the tree.

He is then pictured dead and in a ditch. His body appears to be draped in a Tamil flag.

Although too graphic to show here, the pictures and footage will be broadcast in the documentary Sri Lanka's Killing Fields.

The film will also investigate crimes committed by the Tamil Tigers who are alleged to have used human shields.

Sri Lanka's Killing Fields was screened at the UN Human Rights Council earlier this month.

UN investigation urged

The new evidence follows similar footage broadcast exclusively on Channel 4 News last year depicting the execution of Tamil prisoners by government troops.

Following an investigation, the United Nations concluded the footage authentic.

Earlier this month a UN special envoy said the execution videos appeared to be evidence of "serious international crimes" and urged the international community to investigate.

The Sri Lankan government has vehemently rejected the footage as falsified.

UN Secretary-General Ban Ki-moon has faced growing criticism for refusing to launch an investigation into "credible allegations" that Sri Lankan forces committed war crimes.

A spokesman for Ban Ki-Moon said in April that without the consent of Sri Lanka's government, or a decision by the UN Security Council, General Assembly, Human Rights Council or other international body, a formal investigation of the civilian deaths was not possible.