A rocket or mortar attack on the main U.S. base near Baghdad killed two U.S.-led forces and wounded 40 people, the military said Thursday.

The attack occurred Wednesday at Camp Victory, a sprawling garrison that houses the headquarters of American forces in Iraq, according to a statement.

Two coalition force members were killed and 38 wounded, the military said. It also said two "third country nationals" were wounded. It did not identity them further, but the term usually refers to foreign contractors and not Iraqis.

The attack is under investigation, the statement said.

Most troops stationed at Camp Victory are American but other coalition soldiers are based at the complex near Baghdad International Airport. No further details on the attack were immediately released.