The Iraqi government has started exhuming a mass grave left behind by the Islamic State group in the northwestern Sinjar region in the presence of Nobel Peace Prize laureate Nadia Murad, whose slain relatives are believed to have been buried in the area.

The exhumation, which is being carried out with UN support, began on Friday in the village of Kocho. Murad's official website said it marks the first exhumation of a mass grave containing the remains of Yazidis, a religious minority targeted for extermination by the extremists.

IS militants rampaged across Sinjar in 2014, killing Yazidi men and abducting thousands of women and children. Many followers of the minority faith are still missing, after women were forced into sexual slavery and boys were indoctrinated in jihadi ideology.

"I pay my condolence to the Yazidis and the whole humanity. There is not a single Yazidi family that didn't taste the bitterness of this extermination," said Murad. "They all lost their loved ones, their properties and their dreams, and especially in this village," she said.

Murad was one of an estimated 3,000 Yazidi women and girls who were kidnapped and sold into sexual slavery. She was raped, beaten and tortured before she managed to escape after three months in captivity.