Islamic State militants have released a video purporting to show a boy executing an captive Israeli-Arab, but several key details in the film raise doubts over its authenticity.

The video claims to show the boy, who appears to be no older than 10, carrying out the execution of Muhammad Said Ismail Musallam with a gunshot to the 19-year-old"s forehead 

But heavy editing used to produce the film means it is likely he never pulled the trigger himself and was instead filmed only for scenes to be edited in and around Mr Musallam"s death.

The film shows Mr Musallam describing how he was sent by Israeli intelligence to infiltrate ISIS in Syria, where the group claim he was captured last year.

Wearing an orange jumpsuit, the hostage is later seen kneeling at the feet of two uniformed militants.

The film, like many ISIS execution videos, cuts away without actually showing his killing, and the scene purporting to show the moment of execution is filmed from behind the shooter to avoid identifying him.

During this scene, the shooter"s hand is visible and it clearly appears to be one which belongs to an adult, not a 10-year-old boy.

Islamic State claimed Mr Musallam had posed as a foreign fighter when he joined their ranks last year but later confessed to being an agent for Mossad, the Israeli intelligence agency.