Four US soldiers have been killed by a roadside bomb that exploded near their vehicle in the Iraqi capital, Baghdad, the US military has said.
US troops are engaged in a security crackdown in Baghdad
Two other soldiers were injured in the blast, which happened in an eastern area of the city.
The convoy was returning from search operations when the blast took place, the military said.
Earlier, at least 12 Iraqis were killed in bomb attacks in Baghdad and the city of Iskandariya further south.
Eight Iraqi policemen died when a suicide bomber targeted a joint army and police checkpoint in the Karrada district of Baghdad.
Another 25 people thought to be civilians were injured in the attack.
Four more people were killed in a bomb attack outside a factory in Iskandariya, a centre of the anti-US insurgency to the south of Baghdad.
The US military announced the deaths the four soldiers in a brief statement.
"An improvised explosive device (IED) detonated near the unit's vehicles as they were returning from cordon and search operations," it said.
"The second IED detonated shortly after the initial blast, killing four soldiers and wounding two others."
More than 3,200 US military personnel have died in Iraq since the March 2003 invasion.
The violence came a day after a US military spokesman, Maj-Gen William Caldwell, said that the recent security surge in Baghdad had cut murders and executions by half.
But he said that car bombings in Baghdad and the surrounding area remained a major threat, reaching an "all-time high" in last month.