BEIRUT – A graphic video allegedly showing a Syrian rebel cutting out the heart of a dead pro-government fighter and biting into it sparked outrage Tuesday, reviving concerns about the makeup of opposition forces as Western nations bolster support for fighters on the ground.

The rebel has been identified as Khaled al-Hamad, nicknamed Abu Sakkar, a commander with the Farouq Brigades, based in the central city of Homs and one of the most prominent and organized groups fighting to oust President Bashar al-Assad. The mutilation of corpses is considered a war crime.

The video shows a man bending over a body and cutting open the chest with a knife before standing to face the camera with an organ in each hand. “I swear to God we will eat your hearts and your livers, you soldiers of Bashar the dog,” he declares, before lifting the dead man’s heart to his mouth and biting it, to shouts of “God is great.”

The authenticity of the footage could not be independently verified.

The chilling scene points to the increasingly sectarian nature of the Syrian conflict, which has been marked by revenge killings along religious lines, and highlights complications in efforts to assist fractured opposition military groups.