Displaced people from the minority Yezidi sect, fleeing violence from forces loyal to the Islamic State in Sinjar town, walk towards the Syrian border on August 11, 2014.

© 2014 Reuters

Those who should speak out have not done so.

Seve, a 19-year-old Yazidi woman, has vivid memories of the Islamic State fighter who locked her in his house and tried to rape her after she was kidnapped by IS in August. “He told me his name was Zaid,” Seve said, covering part of her face with her headscarf. “He tried to take me by force.” When Seve fought back, he told her: “I will kill you.”

Seve’s story raises the question of what Muslim religious leaders in the United Kingdom, a recruiting ground for IS, could do to  condemn sexual abuse by the extremist group. IS endorsed sexual slavery on 11th October in its online English-language magazine Dabiq, which targets potential recruits in countries such as the UK, the US and Australia. The article describes the Yazidis, a religious minority, as “infidels.”

“Taking their women as concubines is a firmly established aspect of sharia [Islamic law],” the article says. It brands those who question this as “weak-minded and weak-hearted,” and “apostatising from Islam.”

The evidence continues to grow that IS practices sexual slavery. I met Seve (not her real name) at a shelter near Duhok, in the semi-autonomous region of Iraqi Kurdistan. She showed me a snapshot of her wedding day two years earlier. She wore a white dress and tiara, and leaned close to her husband, tall and slim in a blazer, his hair carefully curled over his forehead. She kissed the photo, then placed it face down beside her and began to cry.

IS shot dead Seve’s husband in front of her before abducting her from her hometown near Sinjar, a Yazidi community in northwest Iraq. The group then imprisoned her with around 2,000 other Yazidi women and girls in a vast hall in the northern city of Mosul. There, she said, she was “married” to Zaid in a group “wedding” with dozens of other captives. “They were tossing sweets at us and taking photos and videos,” Seve said. “The fighters were so happy; they were firing shots in the air.” Several days after the mass marriage ceremony, Seve escaped by fleeing into the night while Zaid slept.

For more than two months after IS’s August rampage through Yazidi communities in northwest Iraq, sceptics, including many Iraqis I interviewed, dismissed accounts such as Seve’s as Shia fabrications to help then Prime Minister Nouri al-Maliki cling to power. Maliki’s government was Shia while IS is Sunni. There was some justification for the doubt—a report that IS was ordering women in Mosul to undergo female genital mutilation, for example, turned out to be bogus.

But denial that women are being traded as sex slaves is impossible. Estimates of the number currently held ranges from several hundred to thousands, according to local activists. On the same day that IS confirmed that it is sexually enslaving female Yazidis, Human Rights Watch released a report I co-authored in which 16 Yazidis who escaped captivity in Sinjar described how their captors detained hundreds of Yazidi women and girls, forcing many into “marriage.”

None of those interviewed by Human Rights Watch said they had been raped. Most claimed they had fought off their armed captors and that others were raped. “They were hitting us and slapping us to make us surrender,” said 17-year-old Adlee. “As much as we could, we didn’t let them touch our bodies.” Yazidi activists told me that the stigma surrounding rape in their community, as well as a fear of reprisal for disclosing sexual violence, makes it likely that some were raped but are afraid to admit it.

There is also evidence of sexual abuse of some of the 500 or more women and girls kidnapped by the Nigerian Islamist group Boko Haram since 2009, among them 276 schoolgirls in April. In a new Human Rights Watch report, 30 women and girls who escaped Boko Haram said they and many other female captives were subjected to abuses including forced marriage and rape, and last week a Boko Haram leader said the extremist group had “married off” the schoolgirls to fighters. The Muslim Council of Britain offered in May to mediate with Boko Haram for the schoolgirls’ release.

Muslim leaders have made some important denunciations of IS. In July, 100 UK imams issued a joint appeal to British Muslims—hundreds of whom reportedly have travelled to Iraq and Syria since 2011—not to fight with IS. The following month, six of the UK’s most influential Muslims issued a fatwa denouncing IS’s beheadings, mass killings, and enslavement of women, children, and minorities, including Yazidis. The religious decree branded British Muslims who join the armed group as “heretics.”

But these same Muslim leaders would do well to speak out again to denounce the sexual component of IS’s enslavement of Yazidi women and girls By doing so they would show their support for women’s and girls’ right to bodily integrity and freedom from torture and cruel, inhuman or degrading treatment. These rights are enshrined in the Universal Declaration of Human Rights. Systematic rape and sexual enslavement are crimes against humanity.

Condemning sexual slavery is not being “weak-hearted.” It’s upholding the basic human rights of women like Seve and Adlee.