MOSUL, Iraq: A Yazidi woman held captive by ISIS militants for more than two years managed to escape when Iraqi forces pushed into Mosul and provided information that helped them retake a neighbourhood of the city, Iraqi commanders said.

The 42-year old woman, who asked to remain unnamed, was kidnapped by the militants from her hometown of Sinjar in the summer of 2014 when they overran northern Iraq and purged its Yazidi minority.

Hundreds of Yazidis were killed and more than 6,000 taken captive by the hard-line Sunni Muslim militants, who regard the Yazidis' faith as devil-worship.

Since then, some have escaped or have been bought back from the militants, but as many as 3,500 remain in ISIS captivity, according to a recent estimate provided by the office that handles kidnappings in the Kurdish region of northern Iraq.

Iraqi forces are now fighting to retake Mosul, the militants' last major stronghold in Iraq, where many Yazidis were held.

The woman, speaking to reporters Friday, said she had been moved from one neighborhood of Mosul to another until her captor fled the city, leaving her with his parents in the Quds neighborhood, which she was finally able to flee.

"I escaped with some families at night, around 3 a.m.," she said in a faint voice, her face completely covered by a black veil covering her face and her hands clasped on her lap.

It was not immediately clear when she escaped captivity but Iraqi forces entered the Quds district on Thursday.

Major General Maan Saadi of the elite Counter Terrorism Service (CTS), which is spearheading the campaign to retake Mosul, said the woman had provided information that helped the operation in the area.

"We took her in with open arms and were able to get some information from her about the neighborhood, which proved useful during our attack and advance on the Quds neighborhood," Saadi said.

Since the offensive began 10 weeks ago, U.S.-backed forces have retaken a quarter of Mosul in the biggest ground operation in Iraq since the 2003 U.S.-led invasion that toppled Saddam Hussein.

Iraqi forces launched a second phase of the offensive this week, pushing from three directions into eastern districts where the battle has been deadlocked for nearly a month.