Four US soldiers were killed today when two helicopters crashed in northern Iraq, American and Iraqi military officials said.
"Four coalition forces members were killed when two aircraft went down in northern Iraq at approximately 2315 GMT yesterday," a US army spokesman said in a statement.
The cause of the incident is unknown and is under investigation, the statement added, without giving any further details.
An Iraqi military official told AFP two helicopters were involved in the incident.
A police official said the helicopters collided near Kirkuk, 255 kilometres north of the capital Baghdad.
The US military is currently taking a back seat to an increasingly large Iraqi force made up of 560,000 policemen and 260,000 military personnel, with the US providing military logistical and air support on request.
According to the Pentagon, 143,000 American troops are deployed in Iraq.
Under an agreement signed between Washington and Baghdad in November, the US military is slated to withdraw its combat troops from Iraq by the end of 2011 and must have them out of cities by the end of this June.