A military spokeswoman had no immediate information.
On Wednesday, U.S. forces and insurgent fighters traded deadly blows, with each side using its weapons of choice: air and artillery power for the Americans, and roadside bombs for their shadowy enemy.
U.S. helicopter gunships backed an artillery bombardment aimed at insurgents in southwest Baghdad, as troops raided homes and arrested a Sunni sheik said to be close to the most wanted man in Iraq.
North of the city, a roadside bomb killed three American soldiers, the U.S. military said.
Baghdad residents said the explosions from the U.S. raid, which were heard from before midnight until about 2 a.m., scared children. Maj. John Frisbie of the 1st Armored Division told The Associated Press that the barrage was aimed at several targets.
He would not elaborate on the targets but said 2nd Brigade made no arrests. Wednesday's barrage could have been a show of force as the military steps up security against threats of attacks over the Christmas holiday by Baghdad's 14 identified guerrilla cells.
In other developments:
Frisbie indicated the military was still acting on information gleaned from the Dec. 13 capture of Saddam Hussein, and residents were also giving information.
"We continue to gain intelligence from the neighborhoods here and the residents of Baghdad who are seemingly frustrated at these continued (rebel) attacks," Frisbie said.
In Washington, Gen. Richard Myers, chairman of the Joint Chiefs of Staff, said Tuesday that information resulting from Saddam's capture led to arrests of 50 former regime leaders the day before. There was a similar surge of information after Saddam's sons, Odai and Qusai, were killed in July, he told reporters at the Pentagon on Tuesday.
"The same phenomenon that happened after his sons were killed is happening again, which is a good sign and it probably tells you the role that fear plays in people's minds," Myers said.
On of the latest targets was Ghazi Hanash, leader of al-Ta'ee tribe based around the northern city of Mosul. He is said to be close to former Vice President Izzat Ibrahim al-Douri, who U.S. commanders say could be organizing the anti-American resistance.
Al-Douri — No. 6 on the U.S. list of the 55 most-wanted Iraqis — is the most senior official of 13 who have escaped custody.
Hanash was arrested at his apartment in Baghdad along with a son and two aides, a cousin, Ghassan Hamadi, said from the Sheik's residence in Mosul.
Before dawn Tuesday, Hamadi said, U.S. troops raided the Mosul house but found only frightened women, who called for help from a cousin living nearby. As the cousin, Mohammed Ajeel, approached the house, he was shot and killed by the Americans, Hamadi said.
It was not immediately possible to get military comment on his report, but U.S. troops have reported the deaths of at least three Iraqis in such attacks in the past week.
U.S. soldiers have arrested dozens of suspected rebels in the past 10 days, including several believed to be recruiting ex-soldiers to attack the U.S. military, their allies and Iraqis working with the U.S.-led occupation.