The ISIS terror group has conscripted approximately 3,500 Iraqis into slavery from the start of 2014 until Oct. 31 of last year, according to a United Nations report released Tuesday. 

The report said that most of that number was comprised of women and children from the Yazidi religious minority captured in the summer of 2014 and forced into sexual slavery.

It said another 800 to 900 children were abducted from Iraq's second largest city, Mosul, for religious and military training. It also said a number of ISIS child soldiers were killed by the extremists when they tried to flee fighting in the western Anbar province.

The report called the civilian death toll "staggering", with at least at least 18,802 Iraqis killed and another 36,245 wounded.  

It also detailed the various methods ISIS has employed to kill its enemies, including public beheadings, running people over with bulldozers, burning them alive and throwing them off buildings.

Such acts are "systematic and widespread ... abuses of international human rights law and humanitarian law," the report said. "These acts may, in some instances, amount to war crimes, crimes against humanity, and possibly genocide."

Iraqi forces have advanced against ISIS on a number of fronts in recent months and driven them out of the western city of Ramadi.

But U.N. envoy Jan Kubis said in a statement that "despite their steady losses to pro-government forces, the scourge of ISIS continues to kill, maim and displace Iraqi civilians in the thousands and to cause untold suffering."

U.N. human rights chief Zeid Raad al-Hussein said the civilian death toll may be considerably higher.

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

ISIS swept across northern and western Iraq in the summer of 2014 and still controls much of Iraq and neighboring Syria. It has set up a self-styled caliphate in the territories under its control, which it governs with a harsh and violent interpretation of Islamic law.

The Associated Press contributed to this report.