A video posted online by Islamic State militants on Tuesday showed a boy killing Muhammad Musallam, an Israeli Arab accused by the group of having signed up as a jihadi to spy for Mossad, with a bullet to the head.
The video, published by the group's Furqan media outlet, showed Musallam sitting in a room wearing an orange jumpsuit, talking about how he had been recruited and trained by the Israeli intelligence service. He said his father and elder brother had encouraged him.
After that, it showed Musallam being escorted to a field and executed by a boy, described by an older, French-speaking fighter as one of the "cubs of the caliphate".
Reuters could not immediately verify the authenticity of the footage, which also appeared on Twitter feeds used by Islamic State supporters.
Israeli security officials said they were aware of the video but could not confirm that it was authentic.
The video, which was about 13 minutes long, showed Musallam on his knees as he listened to the older fighter speaking the verdict in French.
In the video, Musallam repeated what he said last month in an interview published by the group's English language magazine Dabiq, in which he said he had joined Islamic State to report to the Israelis on weapons caches, bases and Palestinian recruits. Israel and his family denied that he was an Israeli spy.
Musallam's family have said he went missing while on a tourist trip to Turkey and an Israeli security official has said he went to Syria to fight for Islamic State in October last year.