A new video released recently on social media by the Islamic State shows children brutally executing more than 25 people described as soldiers of the Syrian regime in the ancient city of Palmyra.

The child executioners, who appear to be between the ages of 12 and 13, wore desert camouflage uniform and brown bandannas.

They stood behind the soldiers who were lined up on their knees on the stage of a Roman amphitheatre.

ISIS fighters can be seen either standing or sitting on top of the ancient ruins, watching over the crowd as they wait for the command to open fire.

An ISIS leader talks to the audience before giving the command to the child executioners to kill the alleged regime soldiers simultaneously by shooting them in the back of the head.

The footage of the slaughter was published online over the weekend through Twitter accounts allegedly connected to ISIS.

The jihadists publicly killed a group of men in the city amphitheatre in late May just after they seized it from government forces, said the Syrian Observatory for Human Rights.

The men were accused of being part of government forces, said the monitoring group.

ISIS often uses children, tagged as "caliphate cubs," as suicide bombers, soldiers and executioners in their bid to spread terror in and out of the Middle East, The Daily Mail wrote.

The group has taken at least 500 children in the previous weeks from Iraq's Anbar and Diyala provinces, taking them to the group's bases where the children are made to train for use in "terror attacks."

"They use children because it is easy to brainwash them," said Rami Abdulrahman, the head of the Syrian Observatory. "They can build these children into what they want. They stop them from going to school and send them to IS schools instead."

According to the Syrian Observatory, while some children are abducted to be trained as fighters, others have been recruited with their parents' approval as part of a "military training exercise."

Children with birth defects are believed to be used by the ISIS as human shields, blood donors for wounded fighters, and suicide bombers.