Fresh US air strikes killed at least 12 people in Baghdad and Basra on Friday as Shiite militiamen and security forces fought sporadic streets battles in the two Iraqi cities.
Six insurgents were killed by US aircraft in the southern port of Basra early on Friday, hours after a Hellfire missile fired from a drone killed six militants in the capital, US and British military officials said.
The strike in Basra happened when US aircraft homed in on the northern Al-Hayanihah district after identifying a group of militants, British spokesman Major Tom Holloway told AFP by telephone.
"The air strike was launched after positively identifying a mortar team that was engaging the Iraqi troops on the ground," Holloway said.
Basra witnessed fierce clashes last month after Prime Minister Nuri al-Maliki ordered a crackdown on Shiite militiamen, mostly from hardline cleric Moqtada al-Sadr's Mahdi Army.
The clashes eased after Sadr ordered his fighters to withdraw from the streets.However, sporadic fighting is still reported from Basra, especially in Hayaniyah.
The US military announced Friday that an unmanned aircraft fired a Hellfire missile and killed six "heavily armed criminals" at around 9:45 pm (1845 GMT) on Thursday.
It said the missile was fired after the drone observed a large group of people with rocket-propelled grenade launchers and mortar tubes.
Two previous air strikes announced by the military on Thursday killed six people in similar cricumstances.
Battles have raged since Sunday between Iraqi and US forces and Shiite fighters from the Mahdi Army in the militia's eastern Baghdad bastion of Sadr City.
Iraqi officials claim around 80 people have been killed, with scores wounded.
Sadr's movement said on Thursday it was "under siege" in the district and warned that its militia was ready to take up arms again, breaking a ceasefire ordered by Sadr last August.
Sadr himself warned earlier this week that the truce would be lifted if security force attacks against his loyalists continued.
The US military says the attacks are targeted at "criminals" firing rockets and mortars into Baghdad neighbourhoods and at the fortified Green Zone where the Iraqi government and the US embassy are based.
Sadr's supporters say the US-led attacks have killed many civilians, including women and children.