At least five people have been killed and more than 45 reported injured in overnight air attacks by US forces in Baghdad's Sadr City suburb.
The explosions were heard for several hours
The US military said in a statement it had carried out "precision strikes" on "enemy positions".
The area is a stronghold for supporters of Shia Muslim cleric Moqtada Sadr, who recently agreed to observe a ceasefire.
At least three Iraqi guardsmen were killed when a car bomb hit their patrol in the northern city of Mosul.
At least three people were wounded in the attack, which happened at about 0900 (0500 GMT), including a civilian.
The latest violence came hours after US Secretary of State Colin Powell warned the conflict in Iraq was getting worse.
He said insurgents wanted to disrupt elections in January, but said the US would increase efforts to defeat them.
New Sadr plan?
Elsewhere in Baghdad, insurgents fired mortar bombs at a police academy in the east of the city. There were no reports of casualties.
But four civilians were killed late on Sunday when their truck ran over a bomb near the town of Baquba, north of the capital.
US troops have frequently clashed with Mr Sadr's Mehdi Army militia.
A peace deal last month ended weeks of fighting in the city of Najaf but clashes have continued in Sadr City.
The BBC's Caroline Hawley in Baghdad says the US believes militants in Sadr City have planted landmines, and these could be the target of the US strikes.
The area is named after Mr Sadr's father, a senior cleric assassinated in 1999 reportedly on the orders of ousted Iraqi leader Saddam Hussein.
On Monday, an aide to Mr Sadr told Arabic TV station al-Jazeera that the cleric planned to announce a new peace plan soon to end the fighting between his supporters and US troops.
Sheikh Hassan al-Adhari, who heads Mr Sadr's office in Sadr City, said the plan "aims to achieve peace in all parts of Iraq and lays out a plan to hold general elections across the country in order to silence those who say it cannot be held because of the security situation".
He did not give details.