Thousands of Yazidis are being held captive by Islamic State in Syria where many are used for sexual slavery or forced to fight for the group, the United Nations said on Wednesday, August 3 on the second anniversary of what investigators termed a genocide, Reuters reports.

A UN-appointed commission of independent war crimes investigators said in June that Islamic State was committing genocide against the Yazidis, a religious community of 400,000 people in northern Iraq, beginning with an attack on their city of Sinjar on Aug. 3, 2014.

Yazidis' beliefs combine elements of several ancient Middle Eastern religions and they are considered infidels by the hardline Sunni Islamist militants.

The UN said most of the captives have been taken to neighboring Syria "where Yazidi women and girls continue to be sexually enslaved and Yazidi boys indoctrinated, trained and used in hostilities."

Around 3,200 Yazidi women and girls are being held captive, and thousands of men and boys are missing, the UN said.

The designation of genocide, rare under international law, would mark the first recognized genocide carried out by non-state actors, rather than a state or paramilitaries acting on its behalf.