In a report, the UN Human Rights Office documents testimonies from 100 people who survived attacks by the militant group in Iraq between June 2014 and February 2015.
The report documents abuses committed by the Sunni militants including killings, torture, rape and sexual slavery, forced religious conversions and the conscription of children.
The UN report also details cases of killings, torture and abductions allegedly carried out by Iraqi security forces and Shiite militias battling the Islamic State militants.
The UN is calling on the Iraqi government to ensure that all accusations are investigated in line with international human rights standards and to publicise the results of the investigations.