“This shocking footage depicts a potential war crime in progress, and demonstrates an utter disregard for international humanitarian law by the armed group in question,” said Ann Harrison, deputy director of Amnesty International’s Middle East and North Africa program.

She said, “We will continue to investigate the incident and once again urge all sides to respect the laws of war and to refrain from torturing, ill-treating or killing their prisoners.”

While much of the video and other evidence filtering out of the Syria conflict has depicted government atrocities against civilians, increasingly there have been instances of abuses against government forces and their sympathizers. On July 31, videos posted on YouTube showed rebels in the northern city of Aleppo executing by ad hoc firing squad several members of a prominent family with close ties to President Bashar al-Assad. The victims died in a 45-second hail of bullets after they were forced to sit along the wall of a local school decorated with a mural of Mickey Mouse and SpongeBob SquarePants.