The United States and the United Nations have expresses 'horror' to a new report that Syria tortured and executed about 11,000 detainees since the uprising began.
The US said that the allegations in the report underscored the need to remove the regime of President Bashar al-Assad.
A Syrian spokesman said the report had no credibility as it was commissioned by Qatar, which funds rebel groups.
According to the BBC, the report comes a day before peace talks are due to begin in Switzerland.
The new report carries torture and execution allegations into a new dimension, revealing that 11,000 victims documented in 55,000 photographs were tortured in one location only.
The report, by three former war crimes prosecutors, 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, the report said.
The photographs cover the period from the start of the uprising in March 2011 until August last year.