US soldiers killed at least 13 people including six Iraqi policemen after coming under fire from a police checkpoint in Baghdad, the US military said.
An Iraqi reporter working for The New York Timeswas also shot dead on his way to work in Baghdad, the newspaper said, a day after two Reuters employees were killed during an incident involving US forces in the city.
Khalid Hassan, 23, was shot in the southern Saidiya district of the capital, the Times said in a statement, adding that the circumstances of the attack were unclear.
A US warplane made a strike during the raid in mainly Shia east Baghdad after US soldiers came under "heavy and accurate" gunfire from a police checkpoint, rooftops and a church, the military said in a statement.
Seven suspected militants were also killed during the clash, in which US soldiers detained an Iraqi police lieutenant on suspicion of planning roadside bomb and mortar attacks on US forces.
The military accused him of links with Iranians accused by Washington of fomenting violence in Iraq.
"When they (US forces) went to arrest this lieutenant, some of the police who were with him began firing on our folks," Marine Gen. Peter Pace, chairman of US military's Joint Chiefs of Staff, told reporters in Washington.
"That turned those individuals into enemy and legitimate folks for our troops to take on in combat."
US commanders say elements of the police are infiltrated by sectarian militia, making it harder to restore security and ease tension between majority Shia and minority Sunni Arabs.
Pace also said that the number of Iraqi army battalions that operate independently, with no assistance from US forces, had dropped from 10 to six over the last two months, although he downplayed the change as partly due to temporary factors.