Iraqi Prime Minister Nouri al-Maliki has vowed to eliminate "all terrorist groups" from Anbar province after al-Qaeda-linked fighters gained control of the town of Fallujah.
Maliki, speaking on state television on Saturday, said his government would end "fitna", or disunity, in the province and would "not back down until we end all terrorist groups and save our people in Anbar".
His comments came after a senior Iraqi security official told the AFP news agency that the government had lost control of Fallujah to fighters from the Islamic State of Iraq and the Levant (ISIL).
The police chief of Anbar, Hadi Razeij, later said the centre of Fallujah had fallen completely into the hands of ISIL fighters. "The walls of the city are in the hands of the police force, but the people of Fallujah are the prisoners of ISIL."
Videos showed ISIL fighters also in control of the main Fallujah highway, and officials and witnesses inside the town told the Reuters news agency that ISIL was in northern and northeastern parts of the town.
|Imran Khan talks about Maliki's options on Anbar violence.
The ISIL has been tightening its grip in the Sunni-dominated desert province, near the Syrian border, in recent months in its effort to create an Islamic state across the Iraqi-Syrian borders.
In Ramadi, the other main city in Anbar, local tribesmen and the Iraqi security forces have worked together to counter the ISIL.
But in Fallujah, the Iraqi army has been prevented from entering by local Sunni tribesmen who, despite not supporting al-Qaeda fighters, are opposed to the Shia dominated government of Maliki.
Al Jazeera's Imran Khan said: "The Iraqi army is on the outskirts of the town, negotiating with tribal leaders to go and fight the ISIL. They need cooperation from the leaders to go in and root out the militants.
"The military had a base just outside, from where they were shelling the city. They have withdrawn from that base and the tribal leaders have moved in, claiming a victory, but it isn’t clear yet from the army if it was rather a tactical withdrawal."
More than 100 people were killed on Friday during fighting in Fallujah and Ramadi, one of the worst days since violence flared when Iraqi police broke up a Sunni protest camp in Anbar on Monday.
The escalating tension shows the civil war in Syria, where mostly Sunni rebels are battling President Bashar al-Assad, who is backed by Shia Iran, is spilling over to other countries such as Iraq, threatening delicate sectarian balances.