A new report has unveiled a "staggering" civilian death toll in Iraq, with nearly 19,000 people killed in less than two years.
At least 18,802 civilians were killed and another 36,245 wounded between January 1 2014 and October 31 2015, according to the UN report.
The report details killings by the Islamic State group including by shooting and beheading, as well as by being burned alive or thrown off buildings.
The report also stated that the Islamic State group is believed to be holding approximately 3,500 people, predominantly women and children from the country's Yazidi minority, captive as slaves.
IS swept across northern and western Iraq in the summer of 2014 plunging the country into its worst political and security crisis since the withdrawal of US troops in 2011.
Another 800 to 900 children were abducted from Iraq's second largest city, Mosul, for religious and military training, the report said, while a number of IS child soldiers were killed by the extremists when they tried to flee fighting in the western Anbar province.
The report said such acts are "systematic and widespread... abuses of international human rights law and humanitarian law", adding: "These acts may, in some instances, amount to war crimes, crimes against humanity, and possibly genocide."
Iraqi forces have advanced against the IS group 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 ISIL continues to kill, maim and displace Iraqi civilians in the thousands and to cause untold suffering."
UN 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.
IS 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 numbers are nowhere near the death tolls recorded during Iraq's bloody civil war. In 2006 alone more than 34,000 civilians were killed, according to UN data.
The following year the Iraqi government refused to provide the UN with death toll statistics, stating that the government wanted to prevent the data from painting a negative image of the country.
But civilian casualties since the rise of IS in Iraq are considerably higher than the preceding years of relative stability. In 2011, the number of civilian deaths due to violence was at its lowest since the civil war, with fewer than 2,800 killed.
"I think this kind of violence will affect our society for the long term," said veteran Iraqi human rights activist Hana Adwar. "The culture of violence is rooted in Iraq now, it's not something that's easy to combat."