Two graves containing the bodies of Iraqi Yazidis believed to have been killed by the Islamic State group have been discovered in northern Iraq, a local official said.

"Two mass graves were found in Um al-Shababik village," Sinjar mayor Mahma Khalil told AFP.

He said the two graves, containing nine bodies each, were about 150 metres from each other, in the western Sinjar region.

Khalil said the authorities were informed and added that the Yazidi Genocide Commission had taken samples.

He said the latest discoveries brought to 29 the number of such graves discovered since anti-IS forces last year retook Sinjar, the minority's main urban hub.

They contain at least 1,600 bodies, he said.

The Kurdish-speaking minority is neither Arab nor Muslim and is mostly based around Sinjar mountain, between the city of Mosul and the Syrian border.

It practices its own religion, a unique blend of faiths which is rooted in Zoroastrianism but borrows from Islam, Christianity and other beliefs.

In August 2014, two months after sweeping across Iraq's Sunni heartland, IS jihadists made a second push into an area that had been under Kurdish security control.

Thousands of Yazidi men were massacred when the jihadists attacked the town of Sinjar and thousands of women and girls were kidnapped and enslaved.

Yazidi community leaders say up to 3,000 Yazidi women may still be at the hands of the jihadists across the "caliphate" they proclaimed more than two years ago over parts of Iraq and Syria.

The UN has called the massacres a genocide, arguing that IS had planned them and then intentionally separated men from women to prevent Yazidi children from being born.