Zainab Bangura visited Iraq and Syria in April and has since been working on an action plan to address the horrific sexual violence against an estimated 3,000 to 5,000 girls enslaved by the terrorist group.
"Girls are sold for "as little as a pack of cigarettes," or for several hundred dollars, up to $1,000, she said."
Abducting girls has become a key part of the ISIS strategy to recruit foreign fighters, who have been traveling to Iraq and Syria in record numbers over the past 18 months.
"This is how they attract young men -- 'We have women waiting for you, virgins that you can marry,'" she told AFP. “The foreign fighters are the backbone of the fighting."
"They kidnap and abduct women when they take areas so they have -- I don't want to call it a fresh supply -- but they have new girls," she said.
"After attacking a village, ISIS splits women from men and executes boys and men aged 14 and over. The women and mothers are separated, she says."
Girls are sold for "as little as a pack of cigarettes," or for several hundred dollars, up to $1,000, she said.
After attacking a village, ISIS splits women from men and executes boys and men aged 14 and over. The women and mothers are separated, she says.
Girls are stripped naked, tested for virginity, and examined for breast size and prettiness. The youngest, and those considered the prettiest, virgins fetch higher prices and are sent to Raqqa, the IS stronghold.
Under the militant's hierarchy, sheikhs get first choice, then emirs, then fighters.
They often take three or four girls each and keep them for a month or so, until they grow tired of a girl. Then she goes back to market.
At slave auctions, buyers haggle fiercely, she says, driving down prices by disparaging girls as flat-chested or unattractive.
"We heard about one girl who was traded 22 times, and another -- who had escaped -- told us that the sheikh who had captured her wrote his name on the back of her hand to show that she was his 'property,'" Bangura said.
Many of the sex slaves are Yazidis, a persecuted minority sect that the ISIS considers to be apostate "devil worshippers," in part because of the Yazidis' ancient connection to the region's pre-Islamic past.
The treatment of Yazidi women, in particular, has been marked by contempt and savagery, Bangura says.
"They commit rape, sexual slavery, forced prostitution, and other acts of extreme brutality," she says.
We heard one case of a 20-year-old girl who was burned alive because she refused to perform an extreme sex act."