Senior members of the Syrian opposition say the government should be prosecuted for war crimes, after evidence emerged of what is being described as the "systematic" killing of 11,000 people.
A team of international law and forensic experts have examined photographs and files smuggled out of Syria, recording killings by government forces at detention centres between March 2011 and August last year.
Many victims showed signs of torture and starvation.
The release of the report comes just as talks are about to begin in Geneva aimed at negotiating an end to Syria's bloody civil war, which began almost three years ago and has left more than 100,000 people dead.
The American State Department has reacted to the newly released photographs by underlining what it calls the need to get the Assad regime out of power. A spokesperson, Marie Harf, condemned the alleged killing of 11-thousand prisoners in the strongest possible terms.
Former chief prosecutor at the Special Court for Sierra Leone, David Crane, who co-authored the report, told Morning Report that the members of the high-powered panel were sceptical to begin with, but were convinced by the evidence.
"We're talking about very experienced people here. Three international criminal lawyers who have prosecuted two heads of state. And then you have very experienced forensic pathologists and an expert in photo imagery, and we looked each other in the eye and said 'this is credible'."
However, the BBC reports that a Syrian spokesman gave the report no credibility saying it was commissioned by Qatar, which funds rebel groups.
A government spokesperson, Bassam Abu Abdullah, said torture has been committed by the rebels.
"We've had professional killers in Syria from around the world. They killed Syrian people, they killed soldiers, they killed policeman. They attacked universities, schools, mosques ... I think those who are practising this kind of torture against people should go to the criminal court, not Syria."
The photographs cover the period from the start of the uprising until August last year. All but one of the bodies shown are male. Investigators say most were emaciated and many had been beaten or strangled.
Prosecutors say such evidence would support findings of crimes against humanity committed by the current Syrian government.