A Yazidi woman who was kept as a sex slave by ISIS for more than two years has been rescued and reunited with her family, Fox News reports.

Gazal, 22, was kidnapped along with her family when ISIS overran the Sinjar region of Iraq in August 2014.

They were first held along with other captured Yazidis in a school, and were later transferred to Mosul. They were given only tiny amounts of food and dirty water, meaning they were forced to drink urine and soon became seriously ill.

Then, ISIS militants began "demanding to know who was still a virgin," Basima, Gazal's 17-year-old sister-in-law, told Fox.

"And from the age of eight, they were taking girls to the market to sell for a cigarette."

Basima and a few others tried disguising themselves as men by cutting their hair off and dressing in male clothing. "We thought that if they mistook us for boys, we would be taken out and killed rather than raped," she said. "But instead, when they knew our trick, the man came in and stripped us in front of everybody. In front of everybody, hundreds, they touched us everywhere, sexually abused us. My father and brother had to watch. And that was the last I saw of them."

The women were transferred to Raqqa, and last year Basima and another sister-in-law, 22-year-old Nadifa, were rescued, but not before suffering torture at the hands of their captors.

Gazal, meanwhile, was chosen by an ISIS militant to be his sex slave. He forced her to convert to Islam, tortured her and raped her. She was then sold on to another fighter, who abused her baby son.

Gazal was finally rescued after her family paid her captor a ransom of $25,000, and last Thursday they were reunited at an IDP camp in northern Iraq.

Yazidism is an offshoot of Zoroastrianism, which blends ancient religious traditions with both Christianity and Islam. ISIS believes them to be "devil-worshippers" and has systematically persecuted members of the faith since its rise to power in 2014. When militants took over the Sinjar region two year ago, up to 5,000 Yazidi men were killed in a series of massacres and thousands of woman and children taken captive. More than 3,000 are still missing.

Amnesty International last month released a damning report that said survivors needed greater support to cope with the long-term implications of their trauma.

Amnesty said that many survivors have been left struggling to pay off huge debts of up to tens of thousands of US dollars after their families borrowed money to pay for their release. An earlier report by the charity found that they often face stigmatisation, and struggle to find husbands, reportedly leading some doctors to perform operations to 'reverse' the loss of virginity.

The majority live in "dire conditions, either with impoverished relatives who have been displaced from their homes, or in camps for internally displaced persons in the Kurdistan Region of Iraq. Their needs outstrip the support available," Amnesty said.

It called for a better system to assess the needs of survivors, and to ensure they receive vital care and support.