Foad, a French truck driver of Moroccan origin, travelled alone through Syria to rescue his 15-year-old sister from an Islamist group she said was holding her captive. But when they finally stood face to face, in tears, she would not leave.

Foad is convinced that his sister Nora, whom he described as an impressionable teen who loved Disney movies before leaving for Syria one afternoon in January, stayed on because she was threatened with execution by the French-speaking commander, or emir, of the group she joined.

The former high school student is among dozens of European girls, many of them her age, living with such groups in Syria. It is an aspect of the conflict that is beginning to worry European governments previously more focused on the flow of young men to join the ranks of Islamic State and others.

Young women are seen as prizes for fighters

Many of the youngest girls are lured with promises of humanitarian work. It is only once in Syria that they discover their fate: forced marriage to a fighter, strict adherence to Islamic law, a life under surveillance and little hope of returning home, say parents, relatives and radicalisation experts.

“When she saw me enter that room, she couldn’t stop crying and holding on to me. At one point I said, ‘So, are you coming back with me?’” Foad, 37, told Reuters. “She started to bang her head against a wall saying, ‘I can’t, I can’t, I can’t’.”

Foad, who asked not to be identified by his full name to protect his family in France, said Nora had told him her first location was in Aleppo. He declined to give the location of their second encounter because he said French police had asked him not to reveal details relevant to investigations.

Foad said a conversation he overheard between his sister and the emir suggested she was warned to stay. Nora had repeatedly asked her family over the phone to be rescued from militants whom she called “hypocrites” and “liars”.

While Western governments have focused on the thousands of male jihadist volunteers who have left for Syria and Iraq, security officials in Europe are expressing alarm about a smaller but steady stream of female groups heading the same way.

Making up about 10 per cent of all departures for Islamist-held areas, according to government officials and terrorism experts, young wo­men are seen as prizes for fighters keen to marry. Teenaged Westerners are often targeted by older, female recruiters, many of whom are based in Europe and use social media, phone calls and false friendships to convince them to do charitable work in war-torn areas.

A video recorded in secret by a woman in the Islamic State-held city of Raqqa in Syria and broadcast last month on France 2 TV gave a glimpse of the reality: women walking in burqas and one called to order by Islamic police for not adequately covering her face. In such an environment the western women have little hope of escaping if they have regrets.

Foad said all contact with his sister had been cut off since his May visit.

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