(CNN) A US Marine was shot and killed while on duty at the Marine Barracks in Washington, DC, early Tuesday morning, the Marine Corps said in a news release.

The fatal injury was not self-inflicted, Marine Gunnery Sgt. John Jackson said.

DC police responded to the incident. The circumstances of the shooting are unclear and the killing is under investigation, the release said.

The Marine, whose identity has not been released, was shot at 5 am. The shooting was determined not to be a threat to local residents because it occurred on the grounds of Marine Barracks, the release said.

CNN has reached out to DC police for comment.