MOSUL — (CNN) Dozens of Yazidi women captured and enslaved by ISIS in 2014 have been moved from Mosul in Iraq to the Syrian city of Raqqa, according to a statement from the UK-based Syrian Observatory for Human Rights.

The Observatory and US military officials have said ISIS militants are fleeing Mosul and heading for Raqqa as tens of thousands of Iraqi-led forces close in on the key city to free it from ISIS control.

The Observatory said dozens of ISIS families have already arrived in Raqqa.

Ethnic cleansing by ISIS has displaced, killed and enslaved hundreds of thousands of Iraqi Yazidis.

Islamic militants captured thousands of Yazidi women and children, and killed the men. ISIS claims the Quran justifies taking non-Muslim women and girls captive, and permits their rape.

The Yazidis, a small Iraqi minority who believe in a single god who created the Earth and left it in the care of a peacock angel, have been subjected to large-scale persecution by ISIS, which accuses them of devil worship.

The United Nations has accused ISIS of committing genocide against the Yazidis.

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