In the footage posted online on Sunday, a man wearing military gear is seen with a knife in his hand slicing parts of a dead soldier's body before turning to the camera and putting the heart in his mouth.

"I swear we will eat from your hearts and livers…," the man says referring to the Syria government soldiers.

Peter Bouckaert of the New York-based Human Rights Watch says the man has been identified as Abu Sakkar, a founder of the militant Farouq Brigade.

“The mutilation of the bodies of enemies is a war crime,” Bouckaert said expressing concern about the war turning into revenge fighting.

Syria has been struggling with a Western-backed insurgency which began in March 2011 as a protesting movement but turned to be a cover for terrorist groups including al-Qaeda and al-Nusra Front.

The United States, Israel, UK and their allies have been supporting the armed insurgency in Syria, mulling ways to supply the militants with more arms to topple the legitimate government of Syrian President Bashar al-Assad.