US aircraft have bombed suspected rebel positions in the Shia area of Sadr City in Baghdad, witnesses said.
US and Iraqi troops frequently clash with Sadr City's Shia militants
American forces have staged regular attacks on the suburb - a stronghold of radical cleric Moqtada Sadr.
The US has not confirmed Monday's raid. But the reports came as Washington promised to crush Iraqi insurgents ahead of elections due in January.
US Defence Secretary Donald Rumsfeld said large-scale assaults would wrest trouble spots from the militants.
"That's what happened in Samarra," he told the Council on Foreign Relations, a New York-based think-tank.
Mr Rumsfeld was referring to the city retaken by coalition and Iraqi forces on Sunday after a two-day assault.
Analysts say Falluja - a centre of Sunni militancy west of Baghdad - and Sadr City may also be on the target list.
"You cannot allow a series of safe havens" for insurgents, the defence secretary said.
Mr Rumsfeld said he did not see civil war as the main danger in Iraq.
Instead, "the risk is that the terrorists... and the people who are running around chopping off people's heads and killing innocent men, women and children will take over" Iraq.
The Defence Secretary's statement came after another day of violence in the country.
At least 20 Iraqis are reported to have been killed and about 100 wounded in a series of bomb attacks.
Central Baghdad was shaken by two powerful car bombs.
The first went off outside an army recruitment centre near an entrance to the high-security Green Zone in the centre of the city.
Less than an hour later, another blast targeted a convoy of cars coming out of a hotel used by foreigners.
Overnight on Monday, one US soldier was killed and two
injured by a roadside bomb near Baghdad.
In the northern city of Mosul, a car bomb attack near a primary school killed at least three people.
The BBC's Caroline Hawley in Baghdad says that although the increasing violence has raised doubts about the elections due in January, a new survey of Iraqis suggests most people remain enthusiastic.
Two blasts rocked Baghdad in the space of an hour
About two-thirds of those asked said it was very likely they would vote with another 25% saying they probably would.
On Sunday night the residents of Falluja, 65km (40 miles) west of Baghdad, endured another night of bombardment from the air.
The US military says precision strikes have inflicted significant damage
on insurgent networks.
But hospital sources said at least nine people were killed, including women and children.