That operation involves 5,000 U.S. troops, Iraqi police commandos, and British soldiers. U.S. and Iraqi troops also raided villages in the area overnight.
The U.S. military says the operation will continue in coming days.
Elsewhere, the U.S. Embassy said today that a U.S. civilian working with the embassy was killed during an attack in Baghdad.
In the southern city of Al-Basrah, police said they arrested five Arab foreign fighters last night who were planning to attack coalition troops and Iraqi police in Al-Basrah.