A US Marine posted at the main gate of a North Carolina base shot and killed a colleague inside a guard shack, a military spokesman says.
Camp Lejeune spokesman Nat Fahy said the shooting occurred early on Tuesday evening.
Police and emergency personnel attempted to revive the shooting victim at the scene, but Fahy said the person was later pronounced dead at a base hospital.
Fahy said the Marine who fired the shot from his M4 rifle was in custody and awaiting questioning by the Naval Criminal Investigative Service.
The name of the shooter, who Fahy said was a male, has not been released. The victim's name was being withheld until relatives were notified.
There were other guards at the gate, but no one else was hurt.
The shooting comes less than a week after a fatal rampage at Fort Hood in Texas, where a soldier is accused of firing 35 shots over an eight-minute span, killing three and wounding 16 others before killing himself.
Fahy stressed the difference in the two situations.
"We understand that people are at a state of heightened sensitivity, given what happened over at Fort Hood,'' Fahy said.
"It's important that we convey that this is not a Fort Hood-like incident. It was an isolated incident that's no longer active."