A Marine standing guard at Camp Lejeune in North Carolina shot and killed another Marine guard with an M4 rifle on Tuesday evening, officials said.
The incident was not thought to be an act of terrorism, nor was it an active-shooter situation, according to a news release from base officials.
Further details, including the names of the Marines involved, were not immediately released.
The shooting comes nearly a week after an Army serviceman went on a rampage at Ft. Hood in Texas, killing three people and wounding 16 more before he killed himself.
The Camp Lejeune shooting happened at 5:30 p.m. at the base's main gate, officials said.
The incident is under investigation by the Naval Criminal Investigative Service.
Camp Lejeune, about 130 miles southeast of Raleigh, is home to the II Marine Expeditionary Force, 2nd Marine Division, 2nd Marine Logistics Group and other combat units and support commands, according to the camp's website.
The camp occupies 156,000 acres and, including the surrounding community, has a population of about 170,000.