Special forces have already conducted operations inside the city, the official said.

The regular army has paused on the edge of the city to allow residents time to leave, after which it will launch "the attack to crush the terrorists".

One option being considered to oust al Qaeda from Falluja would be for army units and tribal fighters to form a "belt" around the city, isolating it and cutting supply routes for militants, military and local officials said.

They would also urge residents to leave the city.

"The siege could take days, we are betting on the time to give people a chance to leave the city, weaken the militants and exhaust them," a senior military officer who declined to be named said.

Iraqi government forces also launched an air strike on Ramadi city on Sunday killing 25 militants, according to local officials.

Fallujah is in the hands of the Al-Qaeda-linked Islamic State of Iraq and the Levant militants, a senior security official said on Saturday.

ISIL militants seized control of the village of Bubali near Ramadi after heavy fighting on Sunday, a witness said.

Government officials in western Anbar province also met tribal leaders to urge them to help repel al Qaeda-linked militants.

Tension has been running high across Anbar since Iraqi police broke up an anti-government protest last week, resulting in deadly clashes.

NJF/NJF