A U.S. soldier opened fire on coalition forces attending a stress clinic at a military base outside of Baghdad International Airport Monday, and at least five were killed, the Pentagon and U.S. Command said.
It was unclear how many U.S. soldiers were killed in the shooting at Camp Liberty, but a defense official said the shooter is alive and in custody. Three were wounded, but it was not immediately clear if the shooter was one of them.
Pentagon officials first indicated that an Army soldier shot the others and then turned the gun on himself.
They spoke on condition of anonymity because the issue is sensitive and details unclear.
There have been several incidents recently when gunmen dressed as Iraqi soldiers have opened fire on American troops, including an attack in the northern city of Mosul on May 2 when two soldiers and the gunman were killed.
The toll from the Monday shooting was the highest for U.S. personnel in a single attack since April 10, when a suicide truck driver killed five American soldiers with a blast near a police headquarters in Mosul. The U.S. death toll in April was 19, the highest in seven months, amid an upsurge of violence in Iraq.
Separately, the military announced Monday that a U.S. soldier was also killed a day earlier when a roadside bomb exploded near his vehicle in Basra province of southern Baghdad.
Attacks on officers, known as fraggings, were not uncommon during the Vietnam war as morale in the ranks sank.
But the only other member of the U.S. military convicted of murdering a superior since the wars in Iraq and Afghanistan began is Army Sgt. Hasan Akbar of the 101st Airborne Division. Akbar was sentenced to death for a 2003 grenade-and-rifle attack at a base in Kuwait before his unit's move into in Iraq.
Also Monday, a senior Iraqi traffic officer was assassinated Monday morning on his way to work in Baghdad. It was the second attack on a high-ranking traffic police officer in the capital in as many days.
A car cut off Brig. Gen. Abdul-Hussein al-Kadhoumi as he drove through a central square in the capital and a second vehicle pulled up alongside and riddled him with bullets, police said, citing witnesses. Al-Kadhoumi was director of operations for the traffic authority.
The gunmen were armed with pistols equipped with silencers, the police added on condition of anonymity because they were not authorized to speak to the media.
Incidents involving gunmen armed with sophisticated weapons, including silencers, have been on the rise since a string of high-profile robberies in April.