Syria is facing fresh war crimes allegations after "clear evidence" of the "systematic torture and killing" of up to 11,000 people was published.

The claims were made by a group of top international lawyers, who were handed 55,000 images of dead prisoners smuggled out of the country by an ex-military policeman.

The lawyers, who are all former war crimes prosecutors, said the photographs showed emaciated corpses with severe injuries and would support findings of crimes against humanity by the Bashar al-Assad regime.

Some detainees appeared to have been beaten, strangled or electrocuted, they claimed.

Desmond De Silva, one of the report's co-authors, described the photographs as "very harrowing" and said victims had suffered the "most awful" injuries.

"These killings were clearly methodical, daily and systematic as a consequence" he said. "They could certainly underpin a charge of crime against humanity".

He added "This industrial killing of people in detention is clearly the work of the Syrian government".

The report, which was commissioned by Qatar, one of the main supporters of the Syrian opposition, was released the day before crucial peace talks are due to get under way.

Officials from around 40 countries are attending, although Iran will not be present after the UN withdrew its invitation.