By Ziad al-Sinjary
MOSUL, Iraq, June 9 (Reuters) - Insurgents overran the headquarters of the provincial government in Iraq's northern city of Mosul late on Monday, making further gains in a fourth day of fighting in the country's second-largest city.
Governor Atheel Nujaifi was trapped inside the building 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.
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.
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.
Police and local officials said the militants were using cranes to move blast walls into position and block roads to prevent the army from regaining control.
Several army officers said Iraqi forces were demoralised and no match for the militants from the Sunni Islamic State in Iraq and the Levant (ISIL), 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 ISIL was only 3 kilometers from the Ghizlani military camp.
The fighting has already forced more than 4,800 families from their homes to other parts of the province and beyond, Iraqi deputy Migration and Displacement minister said. (Reporting by Ziad al-Sinjary; Writing by Ahmed Rasheed; Editing by Isabel Coles and Cynthia Osterman)