Two mass graves containing Yazidi bodies have been discovered in northwestern Iraq, a local official said on Sunday. 

Thousands from the religious minority have been systematically killed, kidnapped and enslaved by ISIS and the graves near the Shababit junction contained at least 18 Yazidis. The bones and identity cards appeared to have been covered over with sandy earth by a bulldozer.

United Nations investigators have said the slaughter of the Yazidi people by ISIS constitutes genocide.

The mayor of Sinjar, Mahma Xelil, said the latest discovery brought the number of Yazidi mass graves found so far to 29, and estimated that the total would rise to more than 40 as ISIS militants were driven back further.

Numbering about 400,000 people, Yazidis are a religious sect whose beliefs combine elements of several ancient Middle Eastern religions and are considered devil-worshippers by ISIS.

The Office of Kidnapped Affairs in Duhok, a department backed by the Kurdistan regional government, says about 3,500 Yazidis are believed to still live in areas controlled by ISIS, many of them women and children.

Last Wednesday, 18 escaped from the town of Tal Afar in northern Iraq as Shi'ite paramilitaries cut it off from the south and west.

But Iraqi Yazidis are barred from resettlement to the UK because the Vulnerable Persons Resettlement Scheme dictates applicants must have Syrian ID documents. ISIS operates indiscriminately on both sides of the Syrian-Iraqi border so for the 90 per cent of Yazidis who are in Iraq, the option of asylum in the UK is unavailable.

Additional reporting from Reuters.