RAMADI, Iraq (AFP) - US marines drove through central Ramadi ordering "terrorists" to surrender or face a crushing assault within hours, as panicked Iraqis began to flee the lawless Sunni Muslim city.

An AFP correspondent said US marines patrolled the centre of Ramadi, using loudspeakers to order all "terrorists" to surrender by 4:00 pm (1200 GMT) or face an assault.

Panicked residents began packing up bare essentials from their homes, before walking and driving away from the city -- the provincial capital of the violence-ridden Al-Anbar province.

Late Saturday, US marines massed in the centre of the city where rebel gunmen patrolled the streets and clashes had earlier killed a policeman.

In the early hours of Saturday, marines had carried out a major offensive called Operation Huricane II to hunt for illegal weapons and ammunition and to disrupt a "terrorist network," the military said in a statement.