The offensive into the district of factories and workshops was an apparent attempt to block armed groups from re-establishing footholds in the city.
Fallujah, about 40 miles (65 kilometers) west of Baghdad, was a hub for al-Qaida in Iraq and other insurgent factions before they were mostly driven out by a Sunni tribal uprising and U.S.-led campaigns more than two years ago. The industrial zone was a center for insurgent bomb-making and rocket production.
Streets were sealed off before Iraqi police and military units swept in, said Fallujah's police chief, Col. Mahmoud al-Issawi. He gave no other immediate details of the operation.
The police action comes two days after a suicide bomber struck an Iraqi military base in Habbaniyah near Fallujah. The blast injured at least 38 Iraqi soldiers
- and was the fourth major attack against Iraqi security forces this month.
In a separate operation, U.S. Marines joined Iraqi security forces in a hunt for weapons caches near Karmah village east of Fallujah, the U.S. military said.