The so-called "Islamic State" is committing genocide against the ancient indigenous Yazidi ethno-religious minority in Iraq and Syria, UN investigators said on Thursday.

The Yazidis are a Kurdish-speaking syncretic religious group living mostly in pockets of Nineveh province and Iraq's Kurdistan Region, whose roots there date back thousands of years to ancient Mesopotamian cultures.

"Genocide has occurred and is ongoing," said the chairman of the UN Commission of Inquiry on Syria, Paulo Pinheiro, in Geneva after unveiling a report.

IS fighters swept through Iraq's Nineveh province in 2014, forcing tens of thousands of Yazidis around their homeland of Sinjar to flee to Iraq's Kurdistan Region. IS killed several thousand Yazidis and forced women into widely documented slavery and sexual exploitation.

The UN said last year that IS may have sought to commit genocide, but Thursday's report was more definitive. It said the extremist group "sought to erase the Yazidis through killings, sexual slavery, enslavement, torture and inhuman and degrading treatment."

IS considers the Yezidis to be devil worshipers.

"Girls as young as nine were raped, as were pregnant women," said the report. "Most of those interviewed reported violent daily rapes by their fighter-owners."

The report said 3,200 Yazidi women and children are still being held by IS, mainly in Syria.

The UN investigators urged the international community to do more to end the genocide and bring those responsible to justice.

Commission member Carla del Ponte, a former prosecutor for international tribunals for Rwanda and the ex-Yugoslavia, said she would be able to "prepare an indictment" for genocide against IS commanders based on the information from the report.

"ISIS has subjected every Yazidi woman, child or man that it has captured to the most horrific of atrocities," Pinheiro said, referring to another acronym for IS.

Self-defense, self-determination and division

The Yazidis' plight triggered a US military intervention against IS in the summer of 2014 after Iraqi Kurdish forces collapsed in Sinjar, leaving thousands of the minority group facing imminent death.

They were saved by a combination of US airstrikes and the intervention of the Kurdistan Workers' Party (PKK), a guerilla group fighting for greater rights and autonomy for Kurds in Turkey.

The collapse of Iraqi Kurdish peshmerga forces was a major embarrassment for Iraqi Kurdish President Masoud Barzani, the main rival of the PKK in the Kurdish nationalist movement.

The fact that Barzani's forces abandoned the Yezidis created major divisions within the community, essentially along the lines of those that support the PKK and those that maintained their support for Barzani.

The PKK responded to the collapse of Sinjar by maintaining forces in the area and setting up Yezidi self-defense groups, thereby bolstering their presence around Mount Sinjar.

The Sinjar Protection Units (HPS) are close to the PKK.

This move further increased tensions between the PKK and Barzani, who also established Yazidi units tied to his Kurdistan Democratic Party.

Despite underlying tensions, a combined Iraqi peshmerga, Yazidi militia, PKK and Syrian Kurdish offensive backed by US airstrikes retook Sinjar in December 2015.

However, competition between the various Kurdish factions complicates the future situation of the Yazidis and their homeland. All this is taking place against the backdrop of the war raging in neighboring Syria, where US-backed Syrian Kurdish forces tied to the PKK have carved out large swaths of territory and begun an experiment in autonomy.

Yazidis tied to the PKK are pushing for Sinjar to become an autonomous province, while Barzani would like to incorporate Sinjar into the Kurdistan Region and wants the PKK to leave. Meanwhile, as time passes and the prospect of returning home looks bleaker, many Yazidis have opted to flee Iraq altogether and seek a better life in Europe.

cw/kl (AFP, dpa)