Members of the al-Qaeda-linked Islamic State in Iraq and Greater Syria (ISIS) took control of Mosul, Iraq's second-largest city, while army troops withdrew from their central base, an Al Arabiya News Channel correspondent reported on Tuesday.
"The city of Mosul is outside the control of the state and at the mercy of the militants," an interior ministry official told Agence France-Presse, making it the second city to fall to anti-government forces this year, Al Arabiya reported.
Militants were making further gains in a fourth day of fighting in the country's second-largest city.
According to Reuters news agency, the city's governor Atheel Nujaifi was trapped inside the provincial government's headquarters but managed to escape while police held back an assault by hundreds of militants armed with rocket-propelled grenades, sniper rifles and heavy machine guns mounted on vehicles.
Earlier on Monday, Nujaifi made a televised plea to the city's inhabitants to fight militants who have been regaining ground in Iraq and last Friday moved into Mosul.
"I call on the men of Mosul to stand firm in their areas and defend them against the outsiders, and to form popular committees through the provincial council," said Nujaifi, the Iraqi flag draped behind him.
The western side of Mosul is now in control of militants, who are advancing steadily southwards in the direction of a major army base where a military airport and top-security prison are located, three army officers told Reuters.
Several army officers told Reuters that Iraqi forces were demoralized and no match for the militants from the ISIS, which is also active across the border in Syria.
"Without urgent intervention of more supporting troops Mosul could fall into their hands in a matter of days" said a senior security official from Nineveh operation center, adding that ISIS was only 3 kilometers from the Ghizlani military camp.
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