Hundreds of U.S. troops are reported to have advanced into the western Iraqi town of Haditha - the second such operation in the region this month.
News reports quote residents as saying troops began their operation before dawn Wednesday, searching homes and detaining suspects.
Earlier this month, U.S. Marines carried out another major operation, targeting militant hideouts near the Syrian border.
Meanwhile, the Al-Qaida in Iraq militant group said Tuesday its leader, Abu Musab al-Zarqawi, has been hurt, and the group called on Muslims to pray for his recovery. The message appeared on the group's website, but its authenticity could not be immediately verified.
The statement did not say where or when Iraq's most wanted terrorist was wounded, but earlier this month there were reports that Zarqawi was had been sighted at a hospital in the western city of Ramadi.
Some information for this report provided by AP and Reuters.