The special session, due to begin at 10:00 am (0800 GMT), comes at the request of Iraq itself, with support from countries and blocs including the Arab Group, the European Union, Iran and the US.
Diplomats from the council's 47 member states are to discuss a draft resolution condemning "in the strongest possible terms systematic violations and abuses of human rights and violations of international humanitarian law resulting from the terrorist acts committed by ISIL (IS) and associated groups."
Their actions since then in several provinces of Iraq "may amount to war crimes and crimes against humanity," the draft resolution said, condemning "all violence against persons based on their religious or ethnic affiliation as well as violence against women and children."
The text calls on the office of the UN's brand new High Commissioner for Human Rights, Jordan's Prince Zeid al-Hussein, to dispatch investigators to Iraq to probe abuses carried out by the group that shocked the world last month with its filmed beheading of US journalist James Foley.
The investigators would be required to give an update to the Human Rights Council at its next regular session which starts next week.
A full report would be expected at the council's most important annual session, scheduled for next February and March.
The text also urges the international community to "strengthen their efforts in assisting Iraq in restoring peace, stability and security in the areas controlled by ISIL and associated groups."
