— The Islamic State extremist organization boasted Sunday that it had enslaved women from an Iraqi minority group in order to use them as concubines, as a rights organization detailed teenagers being bought and sold by fighters for as little as $1,000.

An English-language propaganda magazine for the Islamic State said that Yazidi women and children were considered spoils of war after they were captured as the militants seized their towns and villages. It was the first confirmation from the group of widespread allegations of detention and sexual abuse against Yazidi women.

Hundreds of thousands of members of the ancient sect were displaced as the Islamic State swept through the Sinjar area of northern Iraq in August, prompting President Obama to warn of an unfolding genocide. Those who fled said that while men had been massacred, hundreds of women and children had been detained.

After detaining the Yazidis, the Islamic State systematically separated young women and teenage girls from their families, New York-based Human Rights Watch said in a report that also came out on Sunday.

“The Islamic State’s litany of horrific crimes against the Yazidis in Iraq only keeps growing,” said Fred Abrahams, a special adviser at HRW. The group documented 366 Yazidis who were being held captive but also said some detainees reached by phone reported that the number was more than 1,000. The Iraqi government said that 1,500 women were detained during the advances in the Sinjar area, which is also home to Christian and Shiite minorities.

A 14-year-old girl from Tel Uzer, Iraq in the Nineveh plains area, with the alias "Narin", was given to a member of the Islamic State as his wife. "Narin" escaped and is now hiding in northern Iraqi Kurdistan. (Hassan Haji /Hassan Haji for The Washington Post)

One 15-year-old girl interviewed after she had escaped told the group that the Palestinian Islamic State militant she had been sold to bought her for $1,000.

The women and children were divided among fighters according to Islamic law, the Islamic State magazine, called Dabiq, said.

“The enslaved Yazidi families are now sold by the Islamic State soldiers,” it continued. The article argued that although Christians and Jews can be offered the chance to pay a tax or convert, Yazidis, as polytheists, can be enslaved if captured during war.

It goes on to detail the argument for enslavement under its extremist interpretation of Islam, boasting that it’s the largest mass-enslavement since the early days of the religion.

“One should remember that enslaving the families of the [nonbelievers] and taking their women as concubines is a firmly established aspect of Islamic law,” the magazine said. “Their creed is so deviant from the truth that even cross-worshipping Christians for ages considered them devil worshippers and Satanists.”

The rejection of slavery has led to an increase in adultery and fornication, it said, because men who can’t afford marriage find themselves surrounded by temptation, including by maids. “If she were his concubine, this relationship would be legal,” it said.

None of the Yazidi women interviewed by HRW said they had been raped, but sexual assault is deeply stigmatized in the conservative sect.

One interviewed by the group said she’d seen “brides” taken from both a school and prison she was held in.

“Some were as young as 12 or 13, and up to age 20,” she said. “Some they had to pull away with force. Some of the young women were married but without children, so [the Islamic State soldiers] didn’t believe they were married.”