A video posted online Saturday purportedly shows Islamic State fighters killing at least 25 Syrian government soldiers in the historic town of Palmyra in central Syria.

The video appears to show the soldiers being taken in pickup trucks from the town’s notorious Tadmur prison to the amphitheater. At the theater, they were shot dead by young militants armed with pistols. Hundreds of people were seen watching the killings.

The video didn’t indicate when the killings took place. The Britain-based Syrian Observatory for Human Rights said these shootings too place May 27.

The Associated Press reported in May that scores of Syrian troops and state employees were slaughtered in the days after the terror group captured the town on May 27.

Palmyra is a UNESCO world heritage site famous for its 2,000-year-old Roman colonnades, other ruins and priceless artifacts.

The capture of Palmyra has raised concerns that the militants might try to destroy one of the Middle East’s most spectacular archaeological sites as they have destroyed other pre-Islamic ancient monuments elsewhere in Syria and Iraq.

On Thursday, IS said its militants had destroyed six archaeological pieces from Palmyra that were confiscated from a smuggler.

The shootings in the video took place inside the archaeological site and the troops, some of whom had bruises and blood on their faces apparently as a result of beating, were made to kneel in front of a giant IS black flag before being shot in the back of their heads.

The Associated Press contributed to this report