Tens of thousands of people have fled Iraq's second biggest city Mosul after former al-Qaeda splinter group the Islamic State of Iraq and the Levant (ISIL) took control of the city.

An estimated 1,300 ISIL fighters overran Iraqi security forces and seized the city's airport early on Tuesday. The group stormed provincial government buildings, TV stations, banks and freed an estimated 2,400 prisoners from jails.

Mosul, which has a population of almost two million, is the main export route for Iraq's oil.

In response the Iraqi prime minister Nouri al-Maliki called a national state of emergency after the city and parts of the northern province of Nineveh fell.

"We will not allow Mosul to be under the banner of terrorism, We call on all international organisations to support Iraq and its stance in fighting terrorism. The entire world will suffer if terrorism spreads." Maliki said.

Maliki said the government would arm civilians who volunteered "to defend the homeland and defeat terrorism".

The United States, which invaded Iraq in 2003, condemned the seizure of the city and described the situation as "extremely serious".

"ISIL is not only a threat to the stability of Iraq, but a threat to the entire region," US State Department spokeswoman Jen Psaki said, adding that Washington backed "a strong coordinated response".

Osama al-Nujaifi, Iraq's parliamentary speaker, said Iraqi soldiers abandoned their posts in Mosul when the attack began, action he described as "a dereliction of duty".

Nujaifi said parliament would discuss the call for a state of emergency on Thursday.

Feisal Istrabadi, the former Iraqi ambassador to the United Nations, told Al Jazeera that remnants of the former army could have been involved in the attack.

"I'm hearing sort of word from Baghdad that is quite possible that there are elements of the former Iraqi army that is to say army before 2003 that may be involved in the event in Mosul, and actually it is gone beyond Mosul," Istrabadi said.

Reports by AFP later on Tuesday quoted Iraqi police sources as saying fighters had taken over areas of Kirkuk and Salaheddin province. 

Meanwhile, Syrian activists said ISIL fighters had taken over the Syrian side of al-Yaroubiya crossing, one of three crossings into Iraq. 

'Foreign invasion'

Nujaifi, who is the brother of Atheel al-Nujaifi, the state governor, said he had asked the US ambassador in Baghdad for help in order to stop what he described as "a foreign invasion by ISIL".

Mosul is the second city to be captured by fighters this year after Fallujah.

Al Jazeera's Imran Khan, reporting from Baghdad, said Maliki faced opposition to his call for a state of emergency, which would grant him sweeping powers.

Khan said: "Many politicians have vocally criticised Maliki's handling of the crisis. Many in Iraq are asking why a lightly armed group like ISIL have been able to take over huge cities. 

"Some here worry that a state of emergency will give Maliki sweeping powers that once he has, he may well find difficult to give up."

(Al Jazeera)