His successor Haider al Abadi, deputy speaker of the country's parliament, is a less polarising figure who may be able to unite the country in the fight against the insurgents who have caused a humanitarian crisis by forcing thousands of Christians out of northern Iraq.
Last night's announcement came shortly after President Barack Obama said the US has broken the IS militants' siege and helped rescue thousands of civilians.
Mr Obama said it was unlikely more air drops of food and water would be needed, but that air strikes against the group would continue. He said the US would work with other governments to provide humanitarian relief "wherever we have capabilities" and could reach those in need, even as American warplanes continue a limited campaign of air strikes.
A US military and civilian team of 16 people spent Wednesday on top of Sinjar Mountain to assess conditions and see how many Iraqis needed to be evacuated. They reported that the number of trapped Iraqis was about 4,000 - far fewer than anticipated - and that US-supplied food and water had reached many in recent days.
The United Nations has declared the situation in Iraq a "Level 3 emergency" - a development that will allow for additional assistance to the displaced, said UN special representative Nickolay Mladenov.