BAGHDAD — Two American soldiers were killed and nine were injured Tuesday when a man wearing an Iraqi army uniform opened fire on them inside an Iraqi commando compound in the province of Salahuddin, highlighting the continued danger to U.S. troops in Iraq despite the formal end of combat operations announced by President Obama last week.

The soldiers were members of a security detail protecting a U.S. company commander who was meeting with Iraqi security forces, according to a statement issued by the U.S. military. It wasn’t clear whether the assailant actually was an Iraqi soldier; Iraqi police said the shooting occurred after an altercation between the American soldiers and an Iraqi soldier.

The two deaths are the first U.S. casualties in Iraq since Obama’s Aug. 31 address to the nation on Iraq. But it was the second time that U.S. troops had been caught up in violence in the last week.

On Sunday, U.S. troops joined Iraqi forces to battle seven insurgents attempting to storm an Iraqi army headquarters in downtown Baghdad with bombs and automatic weapons. At least 18 people died, including six of the insurgents. There were no American casualties.

The commander of U.S. forces in northern Iraq, Maj. Gen. Tony Cucolo, described Tuesday’s incident as “”isolated.””

“”This is a tragic and cowardly act, which I firmly believe was an isolated incident and is certainly not reflective of the Iraqi security forces in Salahuddin,”” he said.

The 50,000 U.S. troops who remain in Iraq are combat troops, but they are assigned to what are known as “”advise and assist”” brigades whose job is to aid and guide to Iraqi security forces. Mostly, their job consists of providing protection to the small teams of American advisers and experts assigned to work with Iraqi security forces.

Tuesday’s deaths brought to 20 the number of U.S. soldiers killed in Iraq in hostile incidents this year.