Syria accused of torture and 11,000 executions

One of the authors of the report, that analysed the evidence with regard to torture and execution of persons incarcerated by the current Syrian regime, said that there was evidence of government involvement.

The investigators examined thousands of images of dead prisoners reportedly smuggled out of Syria by a defector.

The report comes a day before peace talks are due to begin in Switzerland. Damascus has denied claims of abuse.

The Guardian - which along with CNN first unveiled the report - says the report's release appears timed to coincide with the conference, in the resort town of Montreux.

The talks are being seen as the biggest diplomatic effort to end the three-year conflict which has left more than 100,000 dead and millions displaced.

The report was commissioned by Qatar, which supports Syrian rebels. It is based on the evidence of a defected military police photographer, referred to only as Caesar, who along with others reportedly smuggled about 55,000 digital images of some 11,000 dead detainees out of Syria.

He told investigators his job had been to take photographs of corpses, both to allow a death certificate to be produced and to confirm that execution orders had been carried out.

"There could be as many as 50 bodies a day to photograph which require 15 to 30 minutes of work per corpse," he is quoted as saying.

He did not claim to have witnessed killings or torture himself, which the investigators said gave weight to his testimony.

The photographs cover the period from the start of the uprising in 2011 until August last year.

Investigators say most of the bodies were emaciated; many had been beaten or strangled.