ISIS militants had accused the man of working for Israeli intelligence

Jihadi shoots him in the back of the head and pushes him into the grave

He is seen standing waist-deep in the sand as he digs his own grave

An Islamic State-affiliated terror cell operating in Egypt has brutally executed a man they accused of being a Mossad spy after first forcing him to dig his own grave.

Graphic and professionally edited footage filmed in Sinai province shows a bearded man wearing an orange jump suit being shot in the back of the head by a masked ISIS militant.

The shocking video has been widely shared by ISIS supporters on social media, who claim the victim had been operating as a spy in Sinai, reporting back to the Israeli government on ISIS' activities in the popular tourist hotspot.

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Victim: The bearded man standing was forced to dig his own grave after being accused of working as a spy for the Israeli intelligence agency Mossad

Sick: The graphic and professionally edited footage filmed in Sinai province shows a bearded man wearing an orange jump suit being shot in the back of the head by a masked ISIS militant

Killer: The executioner pulls out a small handgun and shoots the condemned man in the back of his head

The gruesome video begins with a highly-stylised montage of the man digging his own grave, before cutting to what appears to be the moment he was arrested.

The man is seen wearing a lilac shirt and frantically speaking on the telephone in Arabic while a masked and heavily armed ISIS terrorist sits alongside him.

The footage then shows the same man standing in a deep hole in the desert, being forced to dig his own grave while wearing a Guantanamo Bay-style orange jumpsuit as an ISIS jihadi looks on.

The next harrowing sequence is in slow motion and shows the victim on his knees mumbling to himself while the masked and armed militant stands behind him.

Returning to full speed, the executioner quickly pulls out a small handgun and, without any hesitation, shoots the condemned man in the back of his head.

The final shot shows the victim being pushed into the grave he dug earlier, before his killer uses the same spade to cover the man's body.

Arrested: The man is seen wearing a lilac shirt and frantically speaking on the telephone in Arabic while a masked and heavily armed ISIS terrorist sits alongside him

Prayers: The next harrowing sequence is in slow motion and shows the victim on his knees mumbling to himself while the masked and armed militant stands behind him

ISIS' Sinai branch is just one of several small but deadly cells it has operating outside its so-called caliphate in Syria and Iraq, and its 2,000 members are already known to have been responsible for a string of car bomb attacks earlier in the year.

The group came into in November last year when then region's dominant terror cell Ansar Bait al-Maqdis defected from Al Qaeda and pledged allegiance to ISIS' leader Abu Bakr al-Baghdadi.

The same group are also known to operate inside the Gaza Strip, being the main representative for ISIS' interests in the Palestinian conflict.

Yesterday the group fired rockets in the direction of an airport in the Sinai peninsula used by multinational peacekeeping forces, security sources said, adding that there were no casualties.

The group claimed responsibility for the attack on several Twitter accounts linked to it.

Details of the attack, however, could not be immediately confirmed with some security sources saying the rockets fell inside the airport and others saying they fell outside.

Murdered: Returning to full speed, the executioner quickly pulled out a small handgun and, without any hesitation, shoots the condemned man in the back of his head

Hidden crime: The final shot shows the victim being pushed into the grave he dug earlier, before his killer uses the same spade to cover the man's body

Sinai is where multinational peacekeepers known as the Multinational Force & Observers (MFO) are based. The MFO was created as a result of the 1979 peace treaty between Egypt and Israel.

Egypt's government faces an Islamist insurgency based in Sinai and growing discontent with what critics perceive as heavy-handed security tactics.

Tweets from Twitter accounts linked to Sinai Province claimed responsibility for the last night's attack, saying it came in response to the police arresting a local woman.

ISIS' Sinai branch had so far focused its bombing and shooting attacks on members of Egypt's security forces.

The troops mounted Egypt's toughest crackdown on Islamists after the military removed President Mohamed Mursi of the Muslim Brotherhood from power following mass protests against his rule.

The group also released a recording in May urging attacks against members of the judiciary.