BAGHDAD A U.S. soldier opened fire on fellow troops and at least five were killed Monday, the Pentagon and U.S. Command said.

It was unclear whether the shooter was among the dead in the shooting, which the U.S. Command said in a brief statement occurred about 2 p.m. at Camp Liberty near Baghdad International Airport.

Pentagon officials first indicated that a U.S. Army soldier shot the others and then turned the gun on himself. Later, the officials said it was unclear whether the shooter was among the five dead.

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 b**** exploded near his vehicle in Basra province of southern Baghdad.

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.