International human rights groups have joined Tamil diaspora groups and the UN to call for a full investigation into possible Sri Lankan war crimes.
Their call follows the recent release of a video by Tamil diaspora websites showing the bruised body of a pro-rebel female news reader.
The UN and rights groups say that the probe should also examine alleged crimes committed by Tamil Tiger rebels.
The Sri Lankan military has dismissed the idea of an international inquiry.
It argues that it behaved with complete discipline in the last months of the war.
The video - one of a series that have been released since the end of the Sri Lankan war in May 2009 - appears to show soldiers shooting in the head or legs several naked prisoners whose hands are tied.
The dead bodies of two women are also shown.
Amnesty International and Human Rights Watch say they have verified that one of them was named Isaippiriya, who worked as a television news reader for the Tamil Tigers.
Her body is filmed both clothed and naked.
The TamilNet website says that she was the victim of a "gruesome killing" which amounts to a "war crime committed by the Sri Lanka army".
TamilNet says that she never received any kind of military training and was a hospital volunteer.
Last year Sri Lanka's defence ministry said the same woman was killed in the final battle of the war.
But the rights groups say she and the other prisoners appear to have been executed while unarmed and not in combat.
Sri Lanka's military spokesman, Ubaya Medawala, told the BBC no UN inquiry was needed because there is an ongoing domestic commission looking at the war.
"Let the truth be revealed through that," he said.
Mr Medawala said the army had obeyed the laws of war and had been "truly disciplined".
He also alleged that the video contained doctored material.
It and other excerpts have been broadcast by the Britain's Channel 4 television station.
The footage was deemed authentic by a senior UN official.
Sri Lankan people calling for investigations into alleged war crimes are frequently denounced as traitors.
Meanwhile the Sri Lankan prime minister has made new allegations of war crimes by the Tamil Tigers.
He said four hardcore Tiger members in detention had confessed to executing 60 soldiers towards the close of the war.
Last month the army said it had uncovered a mass grave with the bodies of 26 troops.