At least 12 people have been killed in US air strikes in Baghdad and Basra.
Shia militiamen and security forces have been engaged in sporadic street battles in the two Iraqi cities.
Basra witnessed fierce clashes last month after Prime Minister Nuri al-Maliki ordered a crackdown on Shia militiamen, mostly from cleric Moqtada al-Sadr's Mahdi Army.
The clashes eased after Moqtada al-Sadr ordered his fighters to withdraw from the streets.
An unmanned US aircraft fired a missile and killed what the US said were six 'heavily armed criminals'.
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 US military yesterday killed six people in similar circumstances.
Battles have raged since Sunday between Iraqi and US forces and Shia fighters from the Mahdi Army in the militia's eastern Baghdad suburb of Sadr City.
Iraqi officials claim around 80 people have been killed, with scores wounded.
Moqtada al-Sadr himself warned earlier this week that the truce would be lifted if security force attacks against his loyalists continued.
