Jalila, 12, whose name has been changed for her own protection, told of being separated from her mother and sister and taken to a house in an Isis-controlled part of Syria that had become a "market" of Yazidi women.
"The men would come and select us," she said. "When they came, they would tell us to stand up and then examine our bodies. They would tell us to show our hair and sometimes they beat the girls if they refused. They wore dishdashas [ankle length garments] and had long beards and hair."
Jalila told of being repeatedly raped and then passed or sold to seven Isis fighters before she managed to flee.
Dilara, 20, whose name has also been changed, said she was held in a wedding hall in Syria with 60 other Yazidi female captives.
"From 9.30 in the morning, men would come to buy girls to rape them," she said. "They were like animals. Once they took the girls out, they would rape them and bring them back to exchange for new girls. The ages ranged from 8 to 30 years - only 20 girls remained in the end."
The interviews collected by Human Rights Watch supported the findings of a United Nations investigation last year, which reported the jihadists giving the captured Yazidi women "price tags for the buyers to choose and negotiate the sale".
As many as 3000 people, mainly Yazidis, remain in Isis captivity, according to the UN.
The jihadists attacked the northern Iraqi province of Sinjar last August, overrunning the towns of the Yazidi ethnic minority, whom Isis has labelled "devil worshippers".
After killing hundreds of men, the jihadists rounded up the women in the villages, taking them hostage and sending groups to towns and cities under their control in Iraq and Syria.
Of the 11 women and nine girls interviewed, half - including two 12-year-olds - said they had been raped.
Nearly all said they had been forced into marriage, sold, in some cases several times, or used as "gifts".
The women and girls also saw other captives being abused.
A local doctor told Human Rights Watch that of the 105 women and girls she had examined, 70 appeared to have been raped in Isis captivity.
The interviews are grim confirmation of the boasts by Isis in Dabiq, its English-language magazine, last October in which it tried to provide theological justification for the practice of making the "apostate" Yazidi women the "concubines" of Isis fighters.
The group also circulated a document to its fighters saying it was "permissible to buy, sell, or give as a gift female captives and slaves, for they are merely property, which can be disposed of".
It also said it was "permissible to have intercourse with the female slave who hasn't reached puberty".
Many of the girls who escaped from the jihadists now live in makeshift refugee camps in Kurdish-controlled parts of northern Iraq.
Some of the girls have returned pregnant from their ordeal. Abortion is illegal in Iraq and Human Rights Watch said there was almost no psychological or social support for the Yazidi victims.
The Yazidis
• Religious sect in northern Iraq, Syria and the Caucasus.
• Religion incorporates elements of many faiths, including Zoroastrianism.
• Many Muslims and other groups consider Yazidis as devil worshippers.
• There are about 500,000 Yazidis worldwide
- Telegraph Group Ltd
