Families in Isis' stronghold in Libya are being forced to marry off girls as young as 12 to jihadists in exchange for protection, local doctors and networks have claimed.

Activists say the number of underage marriages is escalating in the city of Derna as foreign fighters continue to infiltrate the area after jihadists pledged allegiance to Isis in October.

Worryingly, clinics are also recording growing numbers of miscarriages and complications during labour and birth as children are taken by fighters as second or third wives. Asmaa Said, a Libyan women’s rights activist, has been collecting data on girls being forced into unions with fighters. Ms Said said establishing how many girls are being married off is complicated by the presence of Isis members in clinics which have been taken over by the group.

Western fighters join Kurds in battle against Isis Show all 9 1 /9 Western fighters join Kurds in battle against Isis Western fighters join Kurds in battle against Isis Foreign Fighters A 67-year old foreign fighter from Canada, nick-named by Kurdish fighters as Hewal Zinar, poses for a photo on April 19, 2015 Uygar Onder Simsek / AFP Western fighters join Kurds in battle against Isis Foreign Fighters A 23-year old fighter and ex-US marine from the US, nick-named by Kurdish fighters as Hewal Agir, guards a look out point during clashes with Islamic State (IS) group fighters on April 17, 2015, in the outskirts of the north-western Syrian town of Tal Tamr AFP Western fighters join Kurds in battle against Isis Foreign Fighters A 26-year old from the US, nick-named by Kurdish fighters as Hewal Dilsad, shows a picture of his wife and son as he poses for a photo on April 14, 2015, in the outskirts of the north-western Syrian town of Tal Tamr Western fighters join Kurds in battle against Isis Foreign Fighters Ex-US marines aged 23 and 24 from the US, nick-named by Kurdish fighters as Hewal Agir (R) and Hewal Agit, guard a position during clashes with Islamic State (IS) group fighters on April 17, 2015, in the outskirts of the north-western Syrian town of Tal Tamr AFP Western fighters join Kurds in battle against Isis Foreign Fighters A group of international foreign fighters pose for a photo on April 16, 2015, in the outskirts of the north-western Syrian town of Tal Tamr AFP/ Getty Images Western fighters join Kurds in battle against Isis Foreign Fighters A foreign fighter poses for a photo with a machine gun on April 19, 2015, in the outskirts of Tal Tamr AFP Western fighters join Kurds in battle against Isis Foreign Fighters A 28-year old foreign fighter from the UK, nick-named by Kurdish fighters as Hewal Baran, poses for a photo on April 19, 2015, in the outskirts of the north-western Syrian town of Tal Tamr, north of Hasakeh AFP/ Getty Images Western fighters join Kurds in battle against Isis Foreign Fighters A 21-year old from the UK and 23 year-old from the US nick-named by Kurdish fighters as Hewal Sores (L) and Hewal Agir guard a post on April 19, 2015 AFP/ Getty Images Western fighters join Kurds in battle against Isis Foreign Fighters A 67-year old man from Canada and a 40-year old from the UK, nick-named by Kurdish fighters as Hewal Zinar (L) and Hewal Cudi train on April 19, 2015, in the outskirts of the Tal Tamr AFP

“Just in the clinics that we are able to monitor, we are seeing four to five cases of under-age brides every week and it’s getting worse. There is also the spread of STDs and the growing prevalence of miscarriages, premature and stillbirths,” she told The Times.

One local gynaecologist said girls are so young they often have no idea what is happing to them. “We see girls who are bleeding heavily from their genital area. Some of them don’t know what sex is — they come into the clinic playing with their dolls.”

An activist in Derna said child weddings were most common in the poorer neighbourhoods of Saida Khadija and Embakh. He said families there had come to perceive marrying their daughters off as a way of protecting them from even worse fates.

“It’s mainly about power and protection — you notice a change in the status of the families," he said. "Before they would hide but after the girls are married to the jihadist commanders they move more easily about town. Some of them get nice cars and nice houses too. They see it as a way of protecting their girls from something worse."