This shocking video appears to show a young boy shooting a 19-year-old "Israeli spy" captured in the Islamic State.

The slickly-produced video shows the boy, who appears to be around 10-years-old, raise a pistol to the kneeling man's head and pull the trigger.

When the victim slumps to the ground, the child shoots him three more times, before saying: "Allahu Akbar!" (God is Greatest).

The film identifies the victim as Muhammad Said Ismail Musallam. In it he describes how he was sent by Israeli intelligence agency Mossad to infiltrate ISIS in Syria.

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.

But the terror group's version of events has been denied by an Israeli security official and the man's parents, who say he went to the war-torn region to fight for ISIS.

Speaking Arabic, Mr Musallam says: "I tell my father and my son: Repent to God. I say to the spies who spy on Islamic State: You will not be successful, they will expose you."

The Israeli Foreign Ministry declined to comment. Israel's Shin Bet internal security agency said that it announced earlier this year that Musalam had left for Turkey to fight with IS.

The Islamic State group last month published a purported interview with Musalam in the militants' online magazine. The man in the magazine's photos looks like the man killed in the video.

Musalam's father, Said, said shortly after the video's release that he had not seen it yet. But he said his 19-year-old son left for Syria four months ago without telling his family.

"I saw him with a long beard and long hair and a Kalashnikov," his father said. "He told me, 'Look dad, I am fed up here, it is a country of war, and I want to come back."'

More than a month ago, the family received a call from an unidentified person who said Musalam had fled IS, was caught at a Turkish checkpoint, and was put in IS jail.

"They did not want to let him leave because if he comes back, he might be caught by the Israelis and tell them what he had seen. So they wanted to get rid of him," the father said. "I know my son. I raised him well. I am sure he's not working for the Mossad."

A previous video released by ISIS' media operation shows a boy of a similar age gun down two men alleged to be Russian spies.

However, a military expert cast doubt on the authenticity of the heavily-edited footage.

Yesterday new anti-terror laws aimed at stopping suspects boarding flights to Syria, Iraq and beyond were agreed by the Commons.

One of the new measures will stop Britons and foreigners who have had their passports seized or are subject to a Terror Prevention and Investigation Measure (Tpim) travelling in and out of the UK.

Airlines will also face civil sanctions if they fail to provide passenger, crew and service information and will also be stopped from flying into the UK if they fail to comply with security directions legislated for this year.

The legislation is an attempt to stem the flow of hundreds of Britons into Syria and Iraq.