They also transported 1,600 people from the town of Hammam Al Alil to Tal Afar, possibly for use as human shields against airstrikes, and told some they may be taken to Syria.
They also took 150 families from Hammam Al Alil to Mosul on Wednesday.
Militants told residents of Hammam Al-Alil that they must hand over their children, especially boys above the age of nine, in an apparent recruitment drive for child soldiers, she said.
ISIS militants were holding nearly 400 Kurdish, Yazidi and Shia women in Tal Afar, and had possibly killed up to 200 people in Mosul city, she said.
The UN also had reports of air strikes causing civilian deaths, including one on Wednesday evening that reportedly killed four women and injured 17 other civilians in the al Qudus neighbourhood in eastern Mosul.
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