Scores of Yazidi mass graves found in Iraq's Sinjar
A total of 1,646 people have been uncovered and investigators expect to unearth another 20 mass graves at the minimum, said Mahma Xelil.
The news came as another mass grave was discovered in the village of Hardan, near Sinjar.
However, Xelil has made exaggerated claims in the past. In November he said that 4,000 Peshmerga fighters had died fighting IS, whereas in December this figure was revised down to 1,600.
A 2016 AP survey of mass graves estimated that up to 15,000 people had been buried in 72 mass graves by IS militants.
Thousands of Yazidi men were murdered after IS militants took control of the Sinjar region because it was believed their religion promoted devil worship.
Thousands of Yazidi women and children were reportedly placed into sexual slavery and abused sexually by IS fighters.
International human rights lawyer, Amal Clooney urged the UN to look into gathering evidence of war crimes, calling the treatment of the Yazidi people "some of the worst crimes of our generation".