The man, identified as Muhammad Said Ismail Musallam, was accused by IS of being a spy.

IS said Mr Musallam, 19, had posed as a foreign fighter when he joined the militants in Syria.

It said he later confessed to being a spy for Israel's Mossad - a charge denied by Israel and by his family.

"Islamic State is doing this because it has an objective: it wants to scare the entire world," said Said Musallam, the man's father.

"How does it want to send that picture to the world - to the entire world and the Arab world? The way is through Muhammad."

He said he son went missing after travelling as a tourist to Turkey in 2014.

A few months later an online magazine linked to IS carried a long interview in his name in which he confessed he had been sent by Israel to infiltrate the organisation.

Its publication was a clear signal that he had fallen foul of the group and was in danger, our correspondent Kevin Connelly says.

The 13-minute video purportedly showing Mr Musallam's death has not been independently verified. Israel has declined to comment.

The video shows a boy aged about 12 accompanied by an older, French-speaking militant. He issued threats against Jews in France before the boy shot an orange-suited figure dead.

It is the latest in a series of IS propaganda videos appearing to show the killing of hostages.

Last month IS militants in Libya released a video showing them beheading 21 Coptic Christians.

(BBC)