The outgoing government has faced criticism that by alienating the Sunni Arab minority, it helped create conditions that revitalised Sunni militants including the Islamic State (IS) jihadist group, which led an offensive that seized much of the Sunni heartland in June.

Washington and the United Nations have repeatedly called on premier-designate Haidar al-Abadi to form a broad-based government.

Giving Sunnis a greater stake in power could help encourage them to join a fightback against the jihadists.

The new UN human rights chief Prince Zeid Ra'ad Al Hussein said the atrocities IS had committed in areas under its control had already shown Sunnis that jihadist rule promised only a "house of blood," while Egypt's prestigious Al-Azhar religious institution also condemned the group.