A former Islamic State [IS] bodyguard of a notorious militant has revealed the depravity of the group's actions in their battle to expand their self-proclaimed caliphate in Iraq and Syria.

The bodyguard of Saddam Jamal, named only as Abu Abdullah, told The Daily Telegraph about his time guarding Jamal in an exclusive interview.

The IS militant was formerly a drug dealer before joining the Free Syrian Army (FSA) and then defecting to IS.

His bodyguard spoke of a series of shocking incidents, including when Jamal forced a mother and father to watch as a fellow jihadist killed their children one at a time.

"Starting with a thirteen-year-old boy, they lined up the sons according to their height and beheaded them in that order," said the bodyguard.

"Afterwards, they hung the boys' heads on the door of the school the family had been hiding in."

Abdullah was clear that, for Jamal, being a militant of IS was not about a higher calling but to obtain more power.

"There are, of course, some who really believe that killing and whipping is the correct way to spread Islam," he told The Daily Telegraph.

"But for Jamal, he doesn't really care if the mission spreads Islam. All he cares about is becoming more powerful. Now, if a stronger organisation emerges, he will join it. And there are lots of men in Isil just like him."

Force, fear and hypocrisy

Abdullah said that Jamal would copy his fellow "emirs" in IS and control their territory through force, fear and hypocrisy.

"They kidnap and carry out assassinations," he said. "They think nothing of bringing down a whole building with women and children inside, just to kill one person.

"A lot of their local and foreign fighters smoke but if they ever catch a civilian doing the same they lock him up, whip him and force them into community service. Why the double standards?"

It is now believed that Jamal is second in command for IS' military affairs, only behind the Chechen "Ginger Jihadist" Abu Omar al-Shishani.

When Jamal was a member of the FSA and the Supreme Military Council that was receiving US funding in Syria, his base in the Deir al-Zour province was attacked by IS, which sent him into hiding.

He next appeared in a video where he pledged allegiance to IS and denounced the FSA fighters as "apostates".

"Isil blew up Jamal's house killing one of his brothers. They kidnapped another brother and killed him too. After that Jamal disappeared," said Abdullah.

The bodyguard's final, shocking tale was of another "emir", named Abu Abdullah al-Qahtani, who used his eight-year-old son to slit the throat of a rival captured by the group.

"He [al-Qahtani] held his son's hand with a knife in it and made him cut the head of an FSA fighter accused of organising attacks on Isil [another name for IS]," he said.

"It would take days to recount to you the violence I witnessed."