Tens of thousands of people have fled Iraq's second biggest city Mosul after the Islamic State of Iraq and the Levant (ISIL), an al-Qaeda splinter group, 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 government buildings, TV stations, banks and freed an estimated 2,400 prisoners from jails in the northern Nineveh province, of which Mosul is the capital.
Mosul, which has a population of almost two million, is also the main export route for Iraq's oil.
|Profile: Islamic State in Iraq and the Levant (ISIL)
Nouri al-Maliki, the Iraqi prime minister, called a national state of emergency after his government lost control of Mosul and parts of Nineveh.
"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.
He said the government would arm civilians who volunteered "to defend the homeland and defeat terrorism".
The US, 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," Jen Psaki, US State Department spokeswoman, said, adding that the US backed "a strong coordinated response".
'Dereliction of duty'
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.
Nujaifi, who is the brother of Atheel al-Nujaifi, Nineveh's 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 faces opposition to his call for a state of emergency, which would grant him sweeping powers.
"Many politicians have vocally criticised Maliki's handling of the crisis," he said.
"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."
Feisal Istrabadi, a former Iraqi ambassador to the UN, told Al Jazeera that remnants of the former army could have been involved in the Nineveh 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 news agency 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.