BAGHDAD, Iraq — Iraqi police announced yesterday the capture of Abu Hamza al-Muhajer, the leader of the Sunni insurgent group Al Qaeda in Iraq, but the U.S. military said it couln’t confirm the report.

Iraqi officials said Mr. Muhajer was apprehended early yesterday after he was found sleeping during a midnight raid of a house in the northern city of Mosul. Mr. Muhajer confessed his identity in an interrogation, a Ministry of Interior spokesman, Major General Abdel-Karim Khalaf, said.

Mr. Muhajer is believed to be an Egyptian, about 40 years old, and an associate of Osama bin Laden’s deputy, Ayman al-Zawahri. He is believed to have taken over the leadership of Al Qaeda in Iraq after the death of Abu Musab al-Zarqawi in an American airstrike in June 2006. Iraqi officials reported in May 2007 that Mr. Muhajer had been killed. His capture yesterday, if true, would be an important boost for Iraqi security forces but may not signify the end of Al Qaeda in Iraq’s presence in the country. Since Zarqawi’s death, the organization has continued killing while pushing its strict interpretation of Islam.

In recent weeks, suicide bombers acting in a manner consistent with previous attacks by Al Qaeda in Iraq have struck funerals, weddings, and police and military checkpoints. The attacks chiefly target Sunnis who have joined forces with the U.S. military.

Also yesterday, militia leaders loyal to the Shiite cleric Moqtada al-Sadr vowed to resist efforts by Iraqi and American forces to relocate residents of some of the most violent parts of Baghdad’s Sadr City neighborhood to camps.

For a month, the densely populated Shiite enclave has served as a battleground in clashes between Mr. Sadr’s Mahdi Army militia and the joint fighting force drawn from the U.S. military and Iraqi security agencies. The battles have generally been taking place in the southwestern quadrant of the rectangular district, an area believed to be the launching site of most rockets targeting the heavily fortified Green Zone.