A New York Times reporter, meanwhile, became the third employee of an international media group to be slain in as many days in Baghdad.
The US forces fought a fierce gunbattle and called in an airstrike after coming under fire during a raid in central Baghdad to arrest a police lieutenant accused of running a terror cell, the military said.
An American unit called in an air strike to protect itself after coming under “heavy and accurate fire” from an Iraqi police checkpoint during the pre-dawn operation.
The strike was sought in order to “prevent further escalation of fire between the Iraqi police checkpoint and coalition forces,” a US military statement said.
“The close air support was directed in front of the Iraqi police, not at them to prevent further casualties,” it added.
The detained “terrorist” led a unit of the Special Groups, the military’s name for Iraqi militant cells supported by the Iranian Revolutionary Guards’ covert Qods Force, the statement said.
The US military says it has proof that the Qods Force is arming and funding Iraqi extremists to attack troops in Iraq, and has sent militants from Lebanon’s Hezbollah militant group to train them.
Tehran denies the charge.
US forces work alongside Iraqi police to train them and prepare them to take over security responsibility in Iraq, but often find their nominal allies are infiltrated by militant and insurgent sympathisers.
Militants, meanwhile, slammed four mortars into the Green Zone on Friday and killed two Iraqi soldiers, local security officials said.
A US embassy official confirmed the explosions in the zone which houses the US and British embassies and the Iraqi parliament, but could not confirm the death toll. There were no American casualties, he said.
The attack was the second this week after a similar shelling on Tuesday killed three people in the zone, including a US soldier.
Eighteen others were also wounded in that barrage, including five Americans — two troops and three contract employees.
The US military alleges that most of the rockets and shells hitting the area are manufactured in Iran and fired from the east Baghdad strongholds of the city’s Shiite militia groups.
An Iraqi journalist working with The New York Times in Baghdad was shot dead on Friday, the newspaper’s Baghdad bureau chief said.
Khalid W. Hassan, 23, was killed while on his way to work in Baghdad’s southern Saidiyah neighbourhood, John Burns said.
“The circumstances of the attack remain unclear at this time,” Burns said.
On Thursday, an Iraqi photographer and his driver working for the international news agency Reuters were killed while filming in Baghdad’s Al-Amin neighbourhood.
Namir Noor-Eldeen, 22, and his driver Saeed Chmagh, 40, died as they were filming a minibus which was hit by a shell or rocket, witnesses said.
A statement from US command said the two were killed during a battle.
“There is no question that coalition forces were clearly engaged in combat operations against a hostile force,” said Lieutenant Colonel Scott Bleichwehl, spokesman for US forces in Baghdad.
Nine insurgents and two civilians were killed in the firefight, the military said, adding “the two civilians were reported as employees for the Reuters news service.”
Paris-based media watchdog Reporters Without Borders claims since the March 2003 invasion, at least 187 journalists, mostly Iraqis, have been killed.
Many have also been caught in the crossfire between opposing sides.
Five people were also killed elsewhere in Iraq on Friday, including three policemen in an attack on their checkpoint near the interior ministry building in central Baghdad, a medic said.
