The city centre of Fallujah has fallen completely into the hands of fighters from the al Qaida-linked Islamic State in Iraq and Levant, the head of police in Iraq's Anbar province said.
Hadi Razeij, head of the Anbar police force, said police had left the city centre entirely and had positioned themselves on the edge of town.
He said on Arabic language broadcaster al-Arabiya: "The walls of the city are in the hands of the police force, but the people of Fallujah are the prisoners of ISIL."
Fallujah, along with nearby provincial capital Ramadi, were strongholds of Sunni insurgents during the US-led war. Al Qaida militants largely took them over earlier this week.
"There will be no retreat until we eliminate this gang and rid the people of Anbar of their evil acts," he said.
"The people of Anbar asked the government for help, they called us to come to rescue them from terrorists."