The stunning assault in Mosul by the al-Qaida-inspired group saw black banner-waving insurgents raid government buildings, push out security forces and capture military vehicles as residents fled for their lives.
Mosul is the capital of Ninevah province. It and the neighboring Sunni-dominated province of Anbar share a long and porous border with Syria, where the Islamic State is also active.
Ninevah Gov. Atheel al-Nujaifi told reporters that "Mosul is capable of getting back on its feet and getting rid of all the outsiders," and said authorities planned to mobilize residents into militias that would play a role in retaking the city.
There were no immediate estimates on how many people were killed in the rampage, which sent an estimated 500,000 people fleeing the city and surrounding areas, according to the International Organization for Migration.
Some simply crossed to the eastern bank of the Tigris River to avoid the worst of the fighting, while others made their way to the Ninevah countryside or sought refuge in the nearby semiautonomous Kurdish region.
Getting into that area has grown trickier, however, with migrants without family members already in the enclave needing to secure permission from Kurdish authorities, according to the IOM.
Foreign Minister Hoshyar Zebari said the fall of Mosul to insurgents must bring the country’s leaders together and deal with the "serious, mortal threat" facing Iraq.
"We can push back on the terrorists … and there would be a closer cooperation between Baghdad and the Kurdistan Regional Government to work together and try to flush out these foreign fighters," he said on the sidelines of a diplomatic meeting in Athens.
Mosul residents reached Wednesday said gunmen went around knocking on doors, reassuring people they would not be harmed and urging civil servants to return to work. The situation appeared calm but tense, said the residents, who would not give their names out of concerns for their safety.
In an eastern section of the city, 34-year-old Ali Sameer said mosques in his neighborhood were calling on people to return to work, especially those in public services.
Al-Maliki has pressed parliament to declare a state of emergency over the Mosul attack.
Echoing al-Maliki, Ninevah governor al-Nujaifi accused senior security force commanders of providing Baghdad with false information about the situation in Mosul and demanded they stand trial.
Speaking from the northern Kurdish city of Irbil where he took refuge, he said smaller armed groups had joined the Islamic State during the fight for control of the city.
Violence raged elsewhere in Iraq on Wednesday.
Police and hospital officials said a suicide bomber set off his explosive belt inside a tent where tribesmen were meeting to solve a tribal dispute in Baghdad’s Shiite Sadr City neighborhood, killing 24 and wounding 41. A car bomb in the district killed four more and wounded nine, while in the northern district of Khazimyah, a car bomb blast in a commercial street killed six people and wounded 14.
A car bomb struck Shiite pilgrims heading to the holy city of Karbala, killing four people and wounding 10, and another killed three people and wounded 12 in a town south of Baghdad.
All officials discussed the attacks on condition of anonymity because they were not authorized to speak to the media.