At least four US soldiers and an Iraqi interpreter have been shot dead by gunmen wearing Iraqi police uniforms, unconfirmed reports say.
Interior ministry officials said the shooting - which has not been independently verified - took place in the northern city of Mosul.
One report says the incident involved one policeman and the translator alone.
The US military says it is investigating the reports, but said it has no information of such an incident.
Iraqi police in Mosul told the BBC two Iraqi policemen reportedly opened fire on US troops in the city, killing between four and six of them. ABC News quoted an interior ministry official as saying an Iraqi interpreter was also killed in the shooting.
However, an Iraqi interior ministry spokesman, Brig Gen Abdul-Karim al-Khalaf, said one Iraqi policeman had shot dead an interpreter, and that no US troops were in the area at the time.