A recently released explicit video from the Islamic State (IS) features a child apparently executing a prisoner who the militants described as a Mossad spy.

Muhammad Said Ismail Musallam was accused of working for the Israeli intelligence agency, and appears to be shot in the head by the child.

The propaganda film purported to tell "a story whose chapters begin in the corridors of Jewish intelligence in the land Israel, and conclude in Dar al-Islam at the feet of the Caliphate's young lions."

Musallam, wearing the orange jumpsuit donned by many of the IS hostages, said that his father and brother encouraged him to join the Mossad, and the family members are named "Mossad agents" in a graphic overlay. Musallam urged his family to "repent," and said that attempts to stop IS would be futile.

The prisoner is then led to a field by a boy whom a French-speaking militant called a "cub of the caliphate."

The French speaker praised the killings at Charlie Hebdo and the Paris grocery store attack, and told Jews that "Allah has gifted us with killing your followers in your own stronghold in France." He also encouraged Muslims in Jerusalem to kill "Mossad spies," and promised that "filth" would be eradicated from the city.

"Mossad cells" are listed after Musallam's apparent execution, including the home and work locations of Musallam's family. The authenticity of the video has not yet been confirmed.

The 19-year-old's family members denied that he was a spy, insisting instead that Musallam willingly joined IS, and was killed for trying to leave.

"I'm sure they brainwashed him," his mother, Hind, said. "He's just a kid. He doesn't know better. They did not give me the chance to hug him or smell him or say goodbye. What kind of people are those. They are the devil."