The investigation team, sent to the region by the UN High Commissioner for Human Rights late last year, said ISIL had committed war crimes, crimes against humanity and genocide in Iraq — all three of the most serious international crimes.
The study specified that ISIL militants were engaged in "killings, torture, rape and sexual slavery, forced religious conversions and the conscription of children."
Attacks on the villages of Yezidi peoples pointed to an intent on the part of ISIL to commit genocide by destroying this ethnic minority, according to the UN investigators.
However, the report also highlights extrajudicial killings, torture and abductions, allegedly carried out by the Iraqi Security Forces and associated militia groups.
On Wednesday, Human Rights Watch issued a report accusing Iraqi security forces and allied militias of destroying houses and other property belonging to civilians following an operation to liberate a northern Iraqi town from ISIL militants.
Islamic State has gained control of vast swaths of Syria and Iraq in recent years and is known for mass killings, including executions of foreign hostages.
In August 2014, a US-led international coalition launched a bombing campaign against ISIL targets in Iraq, later expanding their attacks into Syria.
