Iraqi and US forces raided a Shiite militia stronghold of Baghdad on Monday, triggering a gun battle that left three people dead, while 10 people were killed in a suicide bombing at a funeral in Saddam Hussein's hometown.
A roadside bombing southwest of Baghdad killed three American soldiers late on Sunday, the US military said.
No further details were released. Seven other people were killed and six bodies were found on Sunday.
In Baghdad, sounds of heavy gunfire and explosions rattled the Sadr City district starting about 1 am on Monday and persisted for more than an hour.
Iraqi government television and aides to radical Shiite cleric Muqtada al-Sadr said US aircraft were attacking buildings in the area.
"Several aerial and ground raids began in central Sadr City," al-Sadr aide Jaleel al-Nouri said by telephone as detonations could be heard in the background.
"We can see several houses on fire." The US military said in a statement the fighting started when Iraqi and US forces raided the area to catch extremists suspected of running torture cells.
The forces took fire as soon as they arrived and one US soldier was injured, statement said.
The US military recently reinforced its troop strength in the city to try to reclaim the streets from militias, including al-Sadr's Mahdi Army.
"There's gunfire from all sides," Kadhim al-Mohammedawi, a civil servant who lives in Sadr City, said by telephone. "We can hear women and children screaming."
The district became quiet after more than an hour, except for the sounds of emergency vehicles racing through the streets.
The fighting stopped when Mahdi Army members received calls on their mobile phones, asking them not to confront US troops, said Col. Hassan Chaloub, police chief of Sadr City. It was not clear who made the calls.
He said three people including a woman and a 3-year-old girl were killed and 12 were injured, including five children and two women.
He said three cars and three houses were destroyed in fire. Late on Sunday, scattered clashes broke out between Shiite militiamen and Iraqi soldiers near Hamza Square on the edge of Sadr City, police said.
Two militiamen were killed and five combatants were wounded, including two Iraqi soldiers, police said. The attack on the mourners occurred about 8:15 pm in Tikrit, Saddam's hometown, 130 kms north of Baghdad.
The bomber mingled among the crowd in a funeral hall and detonated an explosive belt, police said.
Police Capt Laith Hamid said the mourners were attending services for the father of a local council member, who was killed in the attack.
Part of the ceiling collapsed and some people might be trapped under the rubble, Hamid said, adding that 10 people were killed and 22 injured.