Islamic State jihadists are still committing genocide against the Yazidi minority in Iraq and Syria, United Nations rights investigators said Thursday.

"Genocide has occurred and is ongoing," Paulo Pinheiro, head of the UN Commission of Inquiry (COI) for Syria, said in a statement.

"ISIS has subjected every Yazidi woman, child or man that it has captured to the most horrific of atrocities," he added, using another acronym for the jihadist group.

The Yazidis are neither Muslims nor Arabs and follow a unique faith despised by IS.

The Kurdish-speaking minority is mostly based around Sinjar mountain in northern Iraq.

In 2014, IS jihadists massacred Yazidis in Sinjar, forcing tens of thousands of them to flee, and capturing thousands of girls and women as spoils of war to be used as sex slaves.

- 'Roadmap to prosecutions' -

The UN warned last year that the group appeared to be committing genocide against the Yazidis, but the COI's report "They came to destroy: ISIS Crimes against the Yazidis", published Thursday, was more conclusive.

The evidence collected by the COI can serve "as a roadmap for prosecutions," commission member Carla del Ponte told reporters.

Del Ponte, previously a prosecutor at international tribunals for Rwanda and the former Yugoslavia, said she would be able "to prepare an indictment" for genocide against IS commanders based on the testimony in the report.

Commission member Vivit Muntarbhorn said IS fighters of multiple nationalities, possibly including Westerners, could be guilty of genocide.

The COI will not release names of potential suspects, but is sharing information with some countries other than Iraq and Syria in an effort to identify foreigners who may be responsible for genocide.

But definitively naming IS leaders based on witness testimony is complicated because many use pseudonyms, the commission said.

Past moves to refer violations in Syria to the International Criminal Court have stalled in the UN Security Council.

The COI members voiced hope that this case would be different because IS is broadly reviled and does not have political support in the Security Council, unlike Syria's government.

- 'A slow death' -

Based partly on interviews with survivors, the report found that IS "sought to erase the Yazidis through killings, sexual slavery, enslavement, torture and inhuman and degrading treatment".

The evidence indicated that IS commanders had laid out clear plans to decimate the Yazidis even before the assault on Sinjar.

By separating men and women, the jihadists took deliberate steps to prevent Yazidi children from being born, which is an element of genocide, the COI said.

IS was holding Yazidis in conditions "that bring about a slow death," and was transferring Yazidi children from their families to live with IS fighters, "cutting them off from beliefs and practices of their own religious community," the report said.

It showed that men and boys over 12 were separated from their families, and those who refused to convert to Islam were killed, while thousands of women and girls, some as young as nine, were sold in slave markets.

The report said some 3,200 Yazidi women and children were currently being held by IS, mainly in Syria, where the females were used as sex slaves and the young boys were being indoctrinated and trained as fighters.