A female ISIS deserter has spoken of how she would revel in torturing other women in front of their family members during her time in an all-girl jihadist brigade in Raqqa, Syria.

The woman, only known as Hajer, also reveals that the British female jihadists would be the most sadistic torturers, and would use a tool known as a 'biter', reportedly able to inflict pain 'worse than childbirth'.

The 25-year-old was one of the first recruits to join the all-female Al-Khansaa brigade in 2014, a group of women jihadists that has been compared to Hitler's Gestapo.

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Evil: The female ISIS deserter, known only as Hajer, reveals how she would enjoy torturing women during her time with Al-Khansaa, pictured

Speaking to writer Ahmad Ibrahim, for Raqqa is Being Slaughtered Silently, Hajer reveals that she joined ISIS because it was one of the few terror groups that allowed women to fight and rise in the ranks.

She was part of the Al-Khansaa brigade, where she would later be joined by runaway London schoolgirls Shamima Begum, Amira Abase and Kadiza Sultana, as well as Muslim convert Sally Jones, 47, from Kent.

The role of Al-Khansaa was - and is - to function as a religious police, ensuring that the residents of Raqqa, Islamic State's so-called 'capital', followed their strict rules.

For those who would break the rules, harsh punishment followed, but Hajer says she did not have an issue administering brutal thrashings.

'I enjoyed it, I enjoyed torturing Syrian women – especially when their fathers or husbands were there,' she told RBSS.

Religious police: The role of Al-Khansaa was - and is - to enforce strict rules for women, and ensure they completely cover themselves and act modestly in Raqqa, pictured

'You know, Europeans are more sadistic and violent than the others. For example, the British female fighters boast of brutal torture. The one who used the "biting" tool is British – pure British. She was known as Um Salama.'

The 'biting' tool has been reported as a favourite among senior members of Al-Khansaa.

Hajer reveals that the British-born female jihadists would use a 'biter', reportedly able to inflict pain 'worse than childbirth'. Pictured is a similar looking plier

The tool has been described as a device similar to a hunting trap - a metal clamping jaw with sharp teeth that cut into the flesh of the victim.

Hajer also revealed that she witnessed the torture and murder of a Jordanian army pilot whose brutal execution shocked the world.

Muath Al-Kasasbeh was captured after his F-16 fighter jet crashed near Raqqa on Christmas Eve 2014.

In January 2015, ISIS released a horrific video showing the 26-year-old being burned alive in a cage.

'I still remember how Um Salama and Um Rayan tortured him. It was the most brutal torturing I have ever seen.'

ISIS has lost an estimated 90 percent of its territory in Iraq and 85 percent in Syria as a result of military campaigns, some of them backed by Western forces.

After US-backed offensives ISIS is all but wiped out in Raqqa, the city they once called their 'capital'.

At one time, the group held around half of Syria, much of it uninhabited desert, but today it controls just 15 percent,