BAGHDAD, Iraq (CNN) -- About 26,000 U.S. and Iraqi forces are taking part in an offensive against al Qaeda in Iraq in northern Iraq, the U.S. military said on Thursday.
Iraqis gather at the site of a U.S. airstrike on Baghdad Thursday. Residents said people were killed in their sleep.
The operation, Lightning Hammer II, is an extension of an earlier operation in Diyala province.
About 14,000 Iraqi security forces stationed throughout Nineveh province and 12,000 U.S. soldiers are conducting the operation, which started Wednesday evening.
The military said the operation "follows Lightning Hammer I ... to deny al Qaeda safe haven in the provinces" of Salaheddin, Nineveh, Diyala, and Kirkuk.
The military said the original Operation Lightning Hammer -- August 13 to September 1 -- ousted militants from the Diyala River valley, northeast of Baquba, the capital of Diyala province.
"Al Qaeda cells were driven from Baquba in Diyala due to Operation Arrowhead Ripper in June and July and then pursued in the Diyala River valley during Operation Lighting Hammer in August," Maj. Gen. Benjamin Mixon, commander of Task Force Lightning and Multinational Division-North.
Also, a U.S. airstrike on the Washash neighborhood in west Baghdad killed at least 14 civilians, an Iraqi Interior Ministry official said Thursday.
The Washash section of the capital is a stronghold of the Mehdi Army militia, which is loyal to Shiite cleric Muqtada al-Sadr. The U.S. airstrike comes at the time al-Sadr has ordered the militants to suspend operations for six months.
The U.S. military confirmed U.S. and Iraqi forces fought militants on the ground and struck targets with what it termed "aerial fire," but made no mention of casualties.
The military said it targeted a Shiite militant cell in Washash that attacked local police, set up illegal checkpoints to kill locals, and killed Sunnis.
After recent deadly fighting between the Shiite rivals Mehdi Army and Badr Organization last week in Karbala, Baghdad, and Babil province, al-Sadr announced he was suspending the militia operations and restructuring the group.
The U.S. military and Iraq back al-Sadr's commitment to stop attacks by his followers.
"Indications are that it appears many honorable members of Jaish al-Mahdi are fulfilling Sadr's pledge of honor to stop attacks and reduce the violence," the military said, using the Arabic name for the Mehdi Army.
However, it said, some groups "are not honoring Sadr's orders and thus will not be subject to the restraint we have observed for those who are responding to Sadr's orders."
Coalition troops also killed six suspected insurgents and detained 25 others in raids Thursday in Tarmiya, Samarra, Tikrit, near Baquba, and Kirkuk, the U.S. military said.
A U.S. soldier died "from a non-battle related cause," on Wednesday, the U.S. military said Thursday. The military is investigating. The soldier is from Multi-National Division-Baghdad. The number of U.S. military deaths is the Iraq war stands at 3,753. The number in September alone is 11. E-mail to a friend