The UN's statement came after the human rights commission in Iraq gathered information about abductions by IS of more than 2,000 women and children and holding them captive.
A commission report said the real figure could be much higher.
In an emergency session of the UN Human Rights Council to address the situation in Iraq, UN Deputy High Commissioner for Human Rights Flavia Pansieri presented the evidence gathered by the agency on the severity of the abuses committed by the extremists.
Pansieri indicated that she had information on the IS violations of human rights and humanitarian law that "may amount to war crimes".
Meanwhile, Chaloka Beyani, the coordinator of human rights organisations within the UN, said the "abducted women contacted the mission and reported that the IS has removed their children and that the women are given to the combatants, sold or enslaved for refusing to convert (to Islam)".
"Many have been directly killed, others deprived of food, water and medicines," Panseri explained.
The organisation has found that women were particularly vulnerable to the abuses of the Islamic extremists who last month announced that all women within the territory they control must cover their faces or face severe punishment.