Almost 19,000 civilians were killed in Iraq between January 2014 and October 2015, according to a new United Nations report released on Tuesday. A further 36,245 civilians were wounded, the report said, branding these findings "obscene".

A significant amount of the brutality has been attributed to ISIS. The militant group is responsible for acts that may "amount to war crimes, crimes against humanity, and possibly genocide", particularly against minorities, the report said.

The UN also estimated that 3,500 people are "currently being held in slavery" by ISIS, which seized mainly Sunni-populated areas in the north and west of Iraq in 2014.

"Those being held are predominantly women and children and come primarily from the Yazidi community," said the joint report by the UN Assistance Mission for Iraq and the UN human rights office. "But a number are also from other ethnic and religious minority communities."

Yazidism is an offshoot of Zoroastrianism, which blends ancient religious traditions with both Christianity and Islam. According to ISIS doctrine, they are "devil-worshippers", and members of the group have been systematically persecuted by militants.

"They use civilians as shields. They use children in armed conflict, they also directly target civilian infrastructure and that can amount to war crimes but they can also constitute crimes against humanity," said Francesco Motta, director of the UN human rights office in Iraq.

Motta said ISIS should face prosecution for international crimes, as the group is seeking to "basically eliminate, purge or destroy minority communities."

Referring to the Yazidi population, who were "basically given the option by ISIL [an alternative name for ISIS] to convert or to be killed", he said the intent was clear: "the international crime of genocide."

The report also detailed the horrific methods ISIS employ to torture and execute people, including shooting, beheading, bulldozing, burning alive and throwing people off buildings. Doctors, teachers and journalists who oppose their ideology have been "singled out and murdered".

"We have a lot of information on the recruitment of children, children as young as nine, to train them sometimes to use them as suicide operatives in their operations, but also forcing them to give blood and also take armed combat roles in other parts where conflict is taking place," Motta said.

According to the report, between 800 and 900 children in Mosul had been abducted for military and religious training.

Ramadi, capital of Anbar province, was recaptured from Islamic State in late December, and the tide of fighting appears to have turned against the group.

"We still have grave fears for civilians in areas under Daesh [ISIS] control as the armed forces and those supporting the government move closer to those areas," Motta said.

UN High Commissioner for Human Rights, Zeid Ra'ad Al Hussein, warned that the civilian death toll may be much higher than the 18,802 recorded:

"Even the obscene casualty figures fail to accurately reflect exactly how terribly civilians are suffering in Iraq," he said.

"The figures capture those who were killed or maimed by overt violence, but countless others have died from the lack of access to basic food, water or medical care."

Additional reporting by Reuters.