As many as 16 mass graves containing the bodies of individuals killed by the Islamic State (Isis) have been discovered in Sinjar in northern Iraq since it was liberated from the control of the terror group, the UN has said. The agency reports about "terrible" and deadly toll on civilians in Isis-controlled areas.

"We have received reports that some 16 mass graves containing the bodies of individuals murdered by ISIL (Islamic State in Iraq and the Levant) have been discovered in Sinjar," spokeswoman for the UN human rights agency, Cecile Pouilly told media in Geneva using another acronym for Isis.

The agency said people, particularly Sunni Arabs, were still being targeted by other ethnic and religious groups who suspect them of supporting the IS. There have been reports of discrimination, harassment, violence and execution in some cases.

"Gross human rights violations continue to be documented in ISIL-controlled areas," she said. "Individuals suspected of disloyalty or of not conforming to the ideology of the group continue to be targeted, and there are reports of kidnappings and the burning and beheading of civilians."

Sunni Arabs are reported to have only limited access to basic services and essential goods, such as water, food, shelter and medical care, Pouilly added, voicing particular concern at the situation of some 1,300 Sunni Arabs stuck near Sinjar in the no-man's-land between Kurdish security forces and the IS.

According to the agency, reports of human rights abuses by Iraqi and Kurdish security forces in the region have also been increasing. "Reports indicate that Iraqi security forces, Kurdish security forces and their respective affiliated militias have been responsible for looting and destruction of property belonging to the Sunni Arab communities, forced evictions, abductions, illegal detention and, in some cases, extra-judicial killings," she said.

"We urge the Government of Iraq to investigate all human rights violations and abuses, including those committed against the Arab Sunni communities, to bring the perpetrators to justice and to ensure that victims have access to appropriate remedies," Pouilly said.