More than 150,000 people have been forced to flee Iraq’s second city of Mosul after Islamist militants effectively took control of it.
Troops were among those fleeing as hundreds of jihadists from the ISIS group overran it and much of the surrounding province of Nineveh.
Iraqi PM Nouri Maliki responded by asking parliament to declare a state of emergency to grant him greater powers.
The US said the development showed ISIS is a threat to the entire region.
US State department spokeswoman Jen Psaki said the situation in Mosul was “extremely serious” and that the US supported “a strong, co-ordinated response to push back against this aggression”.
A spokesman for UN Secretary-General Ban Ki-moon said he was “gravely concerned” at the situation.
He encouraged the Iraqi government and the Kurdish regional government to cooperate in restoring security to region.
Analysis Michael Knights, Washington Institute for Near East Policy
If ISIS were to develop firm control of the city they would have replicated their success in seizing an administrative and economic capital in Syria’s Raqqa province.
In fact, a consolidated ISIS caliphate in western Mosul – with a population of over a million people – would be a far greater success than anything the movement has achieved in Syria and would send shock waves throughout the region.
For this reason we can expect hard fighting to follow as the Iraqi government uses every resource at its disposal – military forces, new local militias, air power, Iranian-backed Shia volunteers from southern militias, the Kurdish Peshmerga plus US intelligence and logistical support.
The battle for Mosul is shaping up to be a critical test of the political and military vitality of the Iraqi state.
Probably only a political-military solution supported by all of Iraq’s factions can restore the situation but it is too soon to gauge whether the Iraqi government recognises this reality.