BBC Online :As many as 500,000 people have been forced to flee the Iraqi city of Mosul after Islamist militants effectively took control of it, the International Organization for Migration says.Troops were among those fleeing as hundreds of jihadists from the ISIS group overran the city and much of the surrounding province of Nineveh.ISIS has now reportedly taken Baiji, home to Iraq’s largest oil refinery.PM Nouri Maliki has asked parliament to declare a state of emergency.The US said the development showed ISIS was a threat to the entire region.ISIS – the Islamic State of Iraq and the Levant, which is also known as ISIL – is an offshoot of al-Qaeda.It now controls considerable territory in eastern Syria and western and central Iraq, in a campaign to set up a militant enclave straddling the border.Residents of Mosul – Iraq’s second city – said jihadist flags were flying from buildings and that the militants had announced over loudspeakers they had “come to liberate” the city.”The situation is chaotic inside the city, and there is nobody to help us,” said government worker Umm Karam. “We are afraid.” Many police stations were reported to have been set on fire and hundreds of detainees set free.”The army forces threw away their weapons, changed their clothes, abandoned their vehicles and left the city,” Mahmud Nuri, a resident fleeing Mosul, told the AFP news agency.The BBC’s Jim Muir says the Iraqi security forces appear to have nothing to fight back against the ISIS militants.Some members of ISIS have also moved on to the nearby town of Baiji, setting the court building and police station on fire and releasing prisoners, according to Reuters news agency.Baiji resident Jasim al-Qaisi told Reuters that the militants phoned tribal leaders in the town and told them: “We are coming to die or control Baiji, so we advise you to ask your sons in the police and army to lay down their weapons and withdraw.”At Baiji’s refinery, which supplies oil products to most Iraqi provinces, many of the guards reportedly agreed to leave and go to another town.US State department spokeswoman Jen Psaki said the situation in Iraq 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.But our correspondent says everything that has happened in Syria indicates that the West would not want to get involved in another Middle East quagmire.Out of media player. Press enter to return or tab to continue.Footage shows ISIS militants driving through the streets of MosulSources have told BBC Arabic that the displaced Mosul residents are heading to three towns in the nearby region of Kurdistan where authorities have set up temporary camps for them.