BAGHDAD — In a stunning assault that exposed Iraq's eroding central authority, al-Qaida-inspired militants overran much of Mosul on Tuesday, seizing government buildings, pushing out security forces and capturing military vehicles as thousands of residents fled the second-largest city.
The rampage by the black banner-waving insurgents was a heavy defeat for Prime Minister Nouri al-Maliki as he tries to hold onto power, and highlighted the growing strength of the Islamic State of Iraq and the Levant. The group has been advancing in both Iraq and neighboring Syria, capturing territory in a campaign to set up a militant enclave straddling the border.
There were no immediate estimates on how many people were killed in the assault, a stark reminder of the reversals in Iraq since U.S. forces left in late 2011.
Earlier this year, Islamic State fighters took control of Fallujah, and government forces have been unable to take it back.
Mosul is a much bigger, more strategic prize. The city and surrounding Ninevah province, which is on the doorstep of Iraq's relatively prosperous Kurdish region, are a major export route for Iraqi oil and a gateway to Syria.
"This isn't Fallujah. This isn't a place you can just cordon off and forget about," said Michael Knights, a regional security analyst at the Washington Institute for Near East Policy. "It's essential to Iraq."
Al-Maliki pressed parliament to declare a state of emergency that would grant him greater powers, saying the public and government must unite "to confront this vicious attack, which will spare no Iraqi." Legal experts said these powers could include imposing curfews, restricting public movements and censoring the media.
State TV said lawmakers would convene Thursday. Parliament speaker Osama al-Nujaifi, a Sunni from Mosul, called the rout "a disaster by any standard."
Regaining Mosul poses a daunting challenge for the Shiite prime minister. The city of about 1.4 milliion has a Sunni Muslim majority and many in the community are already deeply embittered against his Shiite-led government. During the nearly nine-year American presence in the country, Mosul was a major stronghold for al-Qaida. U.S. and Iraqi forces carried out repeated offensives there, regaining a semblance of control but never routing the insurgents entirely.
"It's going to be difficult to reconstitute the forces to clear and hold the city," Knights said. "There aren't a lot of spare forces around Iraq."
White House spokesman Josh Earnest deplored what he called the "despicable" acts of violence against civilians in Mosul. He said Washington is committed to its partnership with Baghdad but is urging the government to take steps to be more inclusive of all Iraqis.
U.N. Secretary-General Ban Ki-moon condemned the attacks across Iraq in recent days "that have killed and wounded scores of civilians." He urged all political leaders "to show national unity against the threats facing Iraq, which can only be addressed on the basis of the constitution and within the democratic political process," according to U.N. spokesman Stephane Dujarric.
Insurgents and Iraqi troops have been fighting for days in Mosul, but the security forces' hold appeared to collapse late Monday night and early Tuesday.
Gunmen overran the Ninevah provincial government building — a key symbol of state control — Monday evening, and the governor fled the city. The fighters stormed police stations, bases and prisons, capturing weapons and freeing inmates. Security forces melted away, abandoning many of their posts, and militants seized large caches of weapons.
They took control of the city's airport and captured helicopters, as well as an airbase 60 kilometers (40 miles) south of the city, the parliament speaker said.
Later Tuesday, Islamic State fighters took over the large town of Hawija, 125 kilometers (75 miles) south of Mosul, according to officials there.
On Tuesday, the militants appeared to hold much of the eastern half of Mosul, which is bisected by the Tigris River. Residents said fighters were raising the black banners that are the emblem of the Islamic State.
Video taken from a car driving through the streets of Mosul and posted online showed burning vehicles in the streets, black-masked gunmen in pickup trucks mounted with anti-aircraft guns, and residents walking with suitcases.