HATTIESBURG, Miss. (AP) _ A tank flipped over during training exercises Thursday, killing three Tennessee national guardsmen and injuring three others.

The officers were among 4,500 Tennessee guardsmen in training at Camp Shelby, said Lt. Lee Elder, public affairs officer for the Tennessee Army National Guard.

A tank carrying the guardsmen flipped when passing over a manmade bridge. Three passengers jumped from the tank, and the other three were killed after being pinned underneath the vehicle, authorities said.

Two of the injured soldiers were in stable condition, one with a back injury, and the other was being held for observation, Elder said.

The soldiers were riding in a M110-A2 self-propelled Howitzer, an artillery cannon that fires shells, said Sgt. Robert Oelze.

''We're not sure what caused it to topple,'' Oelze said. He said the guard and the U.S. Army Safety Center at Ft. Rucker, Ala. were investigating.