Sixteen American troops died in Iraq in the first three days of June, marking a bloody start to the month as the US military presses on with its crackdown on sectarian violence in Baghdad.
A total of 127 American troops died in May, the third worst total for US forces since the invasion of Iraq in March 2003. Fourteen of the latest deaths were reported on Sunday alone by the US military.
North of the capital, a suicide car bomber attacked a police convoy in volatile Diyala province, killing 10 people in a busy market area and wounding 30 others, the local police chief said.
Gunmen at a fake checkpoint near Diyala's provincial capital of Baquba sprayed two minibuses with bullets, killing five people, police said.
Heavy machine gun fire and explosions boomed across central Baghdad late on Saturday from the direction of Sadr City, a sprawling Shi'ite slum and stronghold of radical anti-American cleric Moqtada al-Sadr's feared Mehdi Army militia.
The US military said on Sunday helicopters had strafed militants preparing to fire rockets into the Green Zone, Baghdad's most secure area which houses the Iraqi parliament, many government ministries and the US embassy.
A Reuters journalist saw an air-to-ground missile fired during Saturday's operation.
A US military spokesman in Baghdad, Lieutenant-Colonel Scott Bleichwehl, said helicopters opened fire after gunmen were spotted trying to launch 12 rockets at the Green Zone.