Six Iraqi troops die in US fire

US troops have killed six members of the Iraqi security forces during a patrol on the river Tigris just north of Baghdad, Iraqi police say.

The Americans have given no casualty figures, but have spoken of their regret at the mistake.

The Iraqis say the incident occurred when Iraqi forces fired warning shots into the air as a US boat was passing close to a checkpoint near Tarmiya.

US forces were conducting operations against suspected al-Qaeda militants.

The shootings happened early on Wednesday morning at a joint Iraqi army and police checkpoint.

"The Iraqis fired in the air, but a few minutes later, a helicopter shot at them and killed six of them and wounded 10 others," an Iraqi security official said AFP news agency.

The US military confirmed the incident took place and that coalition aircraft were involved.

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

These killings come at a very sensitive time for relations between the US and Iraqi authorities, says the BBC's Mike Sergeant in Baghdad.

Difficult negotiations are continuing to try to secure an agreement on how long US forces should remain in the country, and on what basis they should operate, our correspondent adds.