CAMP LEJEUNE, N.C. — A Pentagon spokesman says the fatal shooting of a Marine on guard duty at a North Carolina base appears to have been an accident.

Department of Defense spokesman Army Col. Steven Warren told reporters Wednesday that indications point to a “negligent discharge” as the cause of Tuesday’s death in a guard shack at the main gate to Camp Lejeune.

The Marine who fired the single shot from his M4 rifle about 5:30 p.m. remains in custody while the Naval Criminal Investigative Service reviews the incident. He has not been publicly identified.

The victim’s name won’t be made public until at least 24 hours after next-of-kin are notified of the death, following standard military procedure.

Authorities quickly ruled out terrorism, and the base was not placed on lockdown.

A Marine remained in custody Wednesday after military officials say he shot and fatally wounded a colleague with his M4 rifle at the main gate of a North Carolina base.

The shooting happened at 5:30 p.m. Tuesday when the Marine fired on his colleague inside a guard shack at Camp Lejeune, said base spokesman Nat Fahy.

Fahy said law enforcement and emergency personnel attempted to revive the shooting victim, who was shot once, but the victim was later pronounced dead at a base hospital.

The shooting came less than a week after a shooting rampage by a soldier at Fort Hood in Texas killed three and wounded 16 others.

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 It was an isolated incident that’s no longer active.”

Fahy said the Marine who fired the shot from his M4 rifle was in custody and was awaiting questioning by Naval Criminal Investigative Services.

The name of the shooter, who Fahy said was a male, hasn’t been released, and Fahy said the victim’s name is being withheld until relatives are notified. There were other guards at the gate, but no one else was hurt.

The shack is approximately 15 feet by 15 feet and sits under a canopy, Fahy said. He didn’t know if anyone other than the two Marines involved in the shooting were inside the shack at the time.

Fahy said the main gate remained open after the shooting.

He said authorities isolated the area immediately after the shoooting, and when it was determined the situation was secure, traffic was allowed to pass on and off the base.

“At no time was the base ever on lockdown,” Fahy said.