As the Islamic State marched through Iraq and Syria this summer, its refrain was “convert or die.” For many, refusal to swear fealty to the Islamic State and adopt its violent, repressive ideology meant a bullet to the head.

But some women and children imprisoned by the Islamic State who refuse to convert have been dealt a fate some might consider worse than death.

By the end of August, the Islamic State had abducted up to 2,500 Iraqi civilians, most of them women and children, according to a new United Nations report based on more than 450 interviews with witnesses.

Some have been awarded to fighters, others sold as slaves in markets in Mosul, Iraq, and Raqqa, Syria.

There were several reports of an office in Mosul where women and girls are tagged with a price and offered for sale to buyers.

Some women have reportedly been sold to young men to entice them into fighting for the Islamic State.

One Yazidi girl told the U.N. she was taken prisoner after her village was attacked on Aug. 3. She said she was raped several times before she was sold at a market.

In another incident in early August, up to 500 women were taken by the militants as they swept through a Yazidi village in northwestern Iraq. Two days later, 150 of them, mostly from Yazidi and Christian communities, were sold as sex slaves or awarded to Islamic State fighters in Syria.

Married women who did convert were given to fighters as wives after being told their marriages aren’t recognized by Islamic law.

To swell its ranks, the Islamic State is also recruiting teenage boys, the report said, some as young as 13. Witnesses have seen them dressed as militants, wearing masks and carrying weapons. They accompany fighters on patrols and guard prisoners. The number of children seen manning checkpoints dramatically increased in the last few weeks of August, the report said.

Some teenage boys have been forcibly recruited and sent to the front lines to shield militants during fighting, the report said. Others were forced to donate blood to treat injured fighters, according to boys who managed to escape.

As propaganda for its recruitment campaign, the Islamic State reportedly photographed children at a cancer hospital in Mosul holding a black flag and posted them online.

Despite U.S.-led airstrikes intended to weaken militant forces, the Islamic State pushed forward on Thursday, closing in on the Kurdish Syrian border town of Kobane. If it takes the town, it will have unbroken control of a long stretch of the Syria-Turkey border, according to Agence France-Presse.

“The conflict … continues to take a heavy toll on civilians,” the report read. “Gross human rights abuses and acts of violence of an increasingly sectarian nature, committed by armed groups, have exacerbated the effect on civilians and contributed to the deterioration in the human rights situation and the rule of law, in many parts of the country.”