Islamic State militants conducted a mass execution in Palmyra's ancient amphitheater, according to the video uploaded on Saturday (July 4).
Video uploaded to social media purports to show Islamic States militants leading a group of what is said to be Assad soldiers.
The video shows the militants leaving notorious Palmyra prison, where the soldiers were said to be held before the execution.
The soldiers were lead to the ancient amphitheater of Palmyra and lined on stage.
Twenty five men were killed in a shot to their head.
The Syrian Observatory for Human Rights, a UK-based group monitoring the conflict in Syria, reported on May 27 that the Islamic State executed around 20 men in the amphitheater, accusing them of being government supporters.
Palmyra, home to Roman-era ruins, was overran by the Islamic State fighters in May.