Startling details have surfaced of ISIS chiefs giving British women prominent leadership roles in the ultra-religious al-Khanssaa Brigade because they see them as the most committed of the foreign female fighters.

British women are forcing captured Iraqi Yazidi women into sexual slavery at brothels run by the Islamic State of Iraq and Syria (ISIS), according to the Daily Mirror.

Thousands of Iraqi Yazidi women have already been forced into slavery at the brothels. The girls who have been taken captive were all from the Yazidi tribe in Iraq over the course of the militants’ offensive across the region. “These British women are using barbaric interpretations of the Islamic faith to justify their actions,” a source was quoted as saying. “They believe the militants can use these women as they please as they are non-Muslims. It is the British women who have risen to the top of the Islamic State’s Sharia police, and now they are in charge of this operation.”

A top figure in the all female police force is Aqsa Mahmood, 20, of Glasgow. At least five other British females have been identified as members of the group, the Mirror reported.

‘Al-Khanssaa is a Sharia law police brigade. This is ISIS‘ female law enforcement,” Melanie Smith, a research associate at King’s College’s International Centre for the Study of Radicalization, told The Sunday Telegraph in an interview. ‘We think it’s a mixture of British and French women but its social media accounts are run by the British and they are written in English.”

The Daily Mail, meanwhile, reported that more and more young British women are leaving the United Kingdom to join ISIS, and many have formed intense friendships with ISIS fighters. They include twins Salma and Zahra Halane, 16, from Manchester, and mother Khadijah Dare, 22, who is married to a Swedish militant.

ISIS has been on a rampage across Iraq, killing and enslaving members of the country’s ancient religious minorities, including the Yazidis. Previously, two U.N. officials issued a joint statement on the “barbaric acts” of sexual violence committed by ISIS fighters.

“We condemn, in the strongest terms, the explicit targeting of women and children and the barbaric acts the ‘Islamic State of Iraq and the Levant’ has perpetrated on minorities in areas under its control, and we remind all armed groups that acts of sexual violence are grave human rights violations that can be considered as war crimes and crimes against humanity,” said Nickolay Mladenov, a representative of the U.N. secretary-general for Iraq, and Zainab Hawa Bangura, a representative of the secretary-general on sexual violence in conflict.

The U.N. officials’ statement listed evidence of rape being used as weapons of war against women and teenage boys and girls belonging to the Yazidi, Christian, Turkomen and Shabak communities in Iraq.

Middle East expert Haleh Esfandiari has written for the Wall Street Journal that ISIS offers captured girls and women as a “reward” to its followers. “ISIS has received considerable world attention for its savage beheadings, executions of captured soldiers and men in conquered towns and villages, violence against Christians and Shiites, and the destruction of non-Sunni shrines and places of worship,” she said.

“But its barbarity against women has been treated as a side issue. Arab and Muslim governments, vocal on the threat ISIS poses to regional stability, have been virtually silent on ISIS’s systemic degradation, abuse, and humiliation of women.”

“To the men of ISIS, women are an inferior race, to be enjoyed for sex and be discarded, or to be sold off as slaves.”