A video, shared by accounts known to be related with ISIS on Saturday, shows the execution of 25 Syrian regime soldiers in the ancient city of Palmyra's amphitheater .
ISIS announced the men were soldiers who were captured in Homs, a city in western Syria, and shot inside the ancient amphitheater.
Parts from the video showed the shooters to be young boys, possibly at the ages of 13 or 14.
The shooting occurred in front of the amphitheatre at a stage before an ISIS flag, several hundreds watching the killings on the steps.
The soldiers, awaiting to be killed, seem to have been tortured.
ISIS executed 20 men in the same amphitheatre a couple days after capturing Palmyra, also taking control of a military airbase and a prison near it.
UK-based Syrian Observatory for Human Rights said people were forced to gather to watch the shootings.
When the film was videotaped is still not known.
Syria's head of antiquities, Mamoun Abdelkarim, spoke regarding the issue saying, "Using the Roman theatre to execute people proves that these people are against humanity."
There were concerns that ISIS might destroy the ancient remains of Palmyra city, also known as the ‘bride of the desert’, after the group captured it at the end of May.
According to statements from both Syrian state media and the militant group on Friday, ISIS militants destroyed treasures from the ancient Syrian city confirming the concerns.
ISIS controls a large swath of territory from western Syria to eastern Iraq including major cities such as Raqqa and Mosul in Syria and Iraq respectively.
According to UN estimates, over 220,000 people have been killed in Syria since the start of the war that started as an uprise and descended later into a complex civil war. More than 6.7 million people have fled the country while millions of others are displaced internally.