Jihadi John knife
Knife wielding ISIS executioner, Jihadi John, has been named as British national Mohammed Emwazi. (Reuters)

Westerners fighting for the Islamic State (Isis) engage in extreme violence to climb up the jihadi hierarchy that sees them languishing at the bottom, it has been claimed.

A former IS prisoner described the extremist group's structure as divided with national rivalries, explaining that European militants are marginalised and have to go to extreme length to prove their loyalty to the jihadi cause.

"They [the foreign fighters] come ­expecting a heaven and when they see the reality they are shocked," the Syrian man who was detained for six months inside an IS jailed in Al Bab 30km north east of Aleppo, told The Times.

"There is a hierarchy in Isis and the foreign fighters and the Syrians are at the bottom of it."

The former inmate, who regained his freedom through a daring jail-break three months ago and now lives in Turkey, said he suffered the worst beatings and torture sessions from European and fellow Syrian captors attempting to gain respect among the jihadi ranks.

"There are two ways to prove your allegiance to IS: either by getting married or by carrying out the punishments," the man who did not give his real name for fear of reprisals told The Times. "They were merciless — the ­foreign fighters and the ­Syrians treated us the worst because they are the lowest in Isis."

He said was sentenced to death for his involvement with rival moderate rebel groups in Syria and was briefly imprisoned with late Japanese journalist Kenji Goto, who was later transferred to another detention facility in Raqqa.

Goto was eventually beheaded before camera by an infamous masked executioner with a London accent known as Jihadi John, who was recently identified by media as Kuwaiti-born British national Mohammed Emwazi.