A new report claims 70 Arab men, women and children have been killed by Yazidi armed forces in northern Iraq in what has been described as a spate of revenge killings.

The Islamic State (IS) group overran dozens of Yazidi villages in 2014 killing or enslaving an estimated 12,000 men, women and children from the minority religious group.

Thousands of women were sold in markets and forced into sexual slavery, while young boys were sent to IS training camps.

Yazidi survivors say many of their Arab neighbours took part in the kidnapping and killings, making reconciliation between the two groups almost impossible.

The report released by Human Rights Watch (HRW) investigates several instances of Arab men being detained and later found dead. It includes one account in which 53 men, women and children were extrajudicially detained and later executed.

But Yazidi leaders and rights groups have disputed the findings, calling for a more thorough investigation before pointing the finger at Yazidi fighters.

The Yazidi brigades alleged to have carried out the killings, are part of the Popular Mobilization Forces (PMF), which officially joined Iraqi forces to fight IS in the Mosul area one year ago.

Two local men from the Imteywit tribe told HRW that after PMF forces captured the area of Baaj from IS forces, they were loaded into a convoy of seven vehicles along with other local families from the same tribe.

The two men escaped during a stop to change a tyre.

The rest of the group were taken to Qabusiye where the men believe they were killed.

They provided a list of the 22 men, 20 women and 10 children — many of whom were the men's relatives — who have not been seen or heard from since.

A member of the PMF intelligence services said he uncovered several mass graves in that village on December 5.

They contained the bones and skulls of at least four children, tufts of women's hair, and women's and children's shoes and bracelets.

Several Yazidi community leaders confirmed the killings to HRW investigators; one shared photos of the mass graves.

A legal adviser to the Ezidkhan Brigades said that Yazidi forces were involved in the capture of 52 people, but that members of the Imteywit tribe were "dogs who deserve to die".

Lama Fakih, deputy Middle East director at Human Rights Watch, called on Iraqi authorities — who said their own investigations agree with the report — to bring the perpetrators to trail.

"Baghdad needs to assert its authority over the criminal justice process and end armed group vigilantes," Mr Fakih said.

"Past atrocities against the Yazidis don't give its armed forces a free pass to commit abuses against other groups, whatever their past."

'Not a single trial' for Yazidi victims

Yazda, a global Yazidi organization for victims of IS atrocities, said they conducted their own investigations and "found no evidence" of Yazidi revenge killings.

"We know that this alleged event, if it happened at all, happened during a time of total chaos in Sinjar where several militias were operating in the region," Yazda executive director Murad Ismael said.

Mr Ismael said the Yazidi people have received no form of justice for the murders and enslavement of thousands of Yazidis by IS.

While Iraqi authorities investigate this one grave site of Arab victims, 45 Yazidi mass graves and hundreds of killing sites litter the region, he said.

"There has not been even a single trial proceeding with respect to the Yazidi genocide inside Iraq," Mr Ismael said.

"There is a total blockade into any form of justice."

Amal Clooney, who represents victims of IS rapes and kidnappings, has been pushing the Iraqi Government to allow for a UN probe of IS crimes, but to date no charges have been made.

    "There will be no reconciliation without proper justice," Mr Ismael said.

While he disputed the HRW report and strongly opposed revenge violence particularly against women and children, he warned that unless justice was served, revenge may be unavoidable.

"I think there will be revenge, even though Yazidi is a peaceful community not believing in violence," Mr Ismael said.

"The fact that we have thousands of people who have lost family members in this genocide, or have their sisters and mothers raped, or their children taken forcefully from them means we as a community cannot stop all potential revenges."