At least 10 people have been killed in the Iraqi capital, Baghdad, in clashes between US forces and militants in a mainly-Shia district, police say.
Iraqi police said US helicopters were involved in the Shula clashes
The Shula area in north-west Baghdad is a stronghold of the Mehdi Army militia loyal to Shia cleric Moqtada Sadr.
Baghdad doctors said women were among those killed in the fighting.
And in Samarra, about 95km (60 miles) north of Baghdad, at least five people died when suspected al-Qaeda fighters attacked several police stations.
The two battles are a reminder of the continuing twin threat from suspected al-Qaeda fighters and Shia militiamen as the US strives to show its troop build-up is having an effect, says the BBC's Mike Wooldridge in Baghdad.
The fighting in Baghdad erupted in the pre-dawn darkness on Friday.
Iraqi police said US helicopters opened fired during the clash between US troops and militants in the north-western Shula district.
Iraqi police said 10 people had been killed while a doctor in the neighbourhood said his hospital had received 13 bodies, two of them women.
Dr Mohammed Abbas told the French news agency, AFP, that 15 wounded people were also admitted to the al-Noor hospital.
In Samarra, a large number of what the police are officially calling unknown gunmen attacked police checkpoints and a headquarters building at sunset on Thursday.
A Samarra police official told Associated Press news agency that the militants were believed to be al-Qaeda insurgents.
One report said a policeman and two civilians were among those killed in the four hours of fighting.
The clashes come after a Sunni tribal leader was killed in a bomb attack on his house in the town of Kanaan in Diyala province.
Sheikh Yunis al-Tai had been encouraging his community to confront al-Qaeda in Iraq.