BAGHDAD, Sept 3 (Reuters) - U.S. troops killed six Iraqi security personnel on Wednesday, Iraqi police said, in what the U.S. military said was a mistake.

Members of the Iraqi police and army, and a neighbourhood patrol group, fired warning shots in the air when a U.S. boat passed along the Tigris River near their checkpoint close to the town of Tarmiya just north of Baghdad, Iraqi police said.

"The Iraqis fired into the air, not knowing it was a U.S. boat. The U.S. soldiers returned fire and called in air support, and six Iraqis were killed and 10 others injured," said a police source, who declined to be identified.

The U.S. military said there had been an exchange of fire between U.S. troops and Iraqi security forces and the Iraqis suffered casualties. The U.S. military confirmed their aircraft had been involved, but gave no casualty figures.

"It is always regrettable when incidents of mistaken fire occur on the battlefield, a review of the circumstances is under way," the U.S. military said in a statement.

The U.S. soldiers had been conducting operations against suspected al Qaeda militants. (Reporting by Aseel Kami, Writing by Mohammed Abbas: Editing by Andrew Dobbie)

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