A new video released by Islamic State purports to show 25 Syrian soldiers being killed by young militants in the amphitheatre of the ancient city of Palmyra.

The video, which has not been independently verified, was released on social media on Saturday. It shows the men being paraded onto the stage of the amphitheatre and forced to their knees in front of a large black IS flag.

They were killed by 25 militants, some of whom may have been as young as 13 or 14, according to the BBC. The militants were dressed in camouflage with brown bandanas.

The group claimed that the men executed had been captured in the city of Homs.

Hundreds of men and some children in civilian clothing are shown in the video sitting on the steps of the Roman amphitheatre, watching the executions.

It is well known that IS has recruited children, and at the beginning of June it was reported that they had captured as many as 500 children in recent weeks.

The UK-based Syrian Observatory for Human Rights has suggested that the execution took place on May 27, a week after ISIS took control of the UNESCO world heritage site, based on civilian reports from the time. These reports suggested that about 20 people had been killed and it is not clear whether they are separate incidents.

Syria's head of antiquities, Mamoun Abdelkarim, said in May that "Using the Roman theatre to execute people proves that these people are against humanity."

There were fears that IS would destroy the ancient city as they have destroyed other UNESCO world heritage sites and relics, but the majority of the famous sites at Palmyra have so far been preserved. According to the Guardian, the group said in May that they would keep the ruins intact but would "destroy the idols".

Last month it was reported that they had destroyed the Lion of al-Lat statue, which dated back to the 1st century BC. It was also said that they had planted explosives in the ruins.