Iraqi Yazidis are carrying out "revenge" attacks on Arab villagers they believe to have sided with Islamic State militants during persecution of the minority group last year, it has been claimed.

Sunni Muslims living in Sinjar told Reuters that armed Yazidis have attacked four villages in the past two weeks, killing 21 people. A further 17 are still missing.

One local labelled it "an act of revenge by the Yazidis".

"The aim is to expel Arabs from the area so that only Yazidis remain," 41-year-old Dhafer Ali Hussein from Sibaya, one of the affected villages," said. "They want to change the map."

A minority ethno-religious group in Iraq, Yazidis have been systematically persecuted by Islamic State during its attempts to create a caliphate. Their religion is an offshoot from Zoroastrianism, which blends ancient religious traditions with both Christianity and Islam. IS insurgents believe them to be "devil-worshippers".

Hundreds of them were killed and thousands more captured, made slaves and raped last year.

Human Rights Watch reported in October 2014 that hundreds of Yazidi men, women and children were being held in "makeshift detention facilities" in Iraq and Syria. Many had been forced to convert to Islam, while others had been sexually abused, raped, and girls in their teens taken as wives for jihadists.

"The Islamic State's litany of horrific crimes against the Yazidis in Iraq only keeps growing. We heard shocking stories of forced religious conversions, forced marriage, and even sexual assault and slavery," special adviser at HRW Fred Abrahams said.

He added that some of the victims were children.

Reuters reports that Yazidis, many of whom fled the Sinjar region in the north of Iraq last year, are now returning home and "uncovering one mass grave after another" as the extent of the atrocities committed by IS militants becomes apparent. The remains of more than 40 Yazidis were found in two "bloodstained pits" just last week.

Some members of the minority are now blaming local Arabs for aiding the militants, "looting their possessions and actively participating in what they call attempted genocide". Though villagers living in Sibaya admitted that some men had joined IS, they said those men have since fled, or were killed when Kurdish peshmerga fighters forced Islamic State out of the area in December.

There are now fears that tensions between these groups may add to the crisis perpetrated by IS.