A civilian approaching the USS Mahan, a U.S. Navy destroyer at the world's largest naval base, took a weapon from a sailor who was standing watch and used it to shoot and kill another sailor who was trying to help his embattled colleague, Navy officials said Tuesday.

Navy security forces then killed the suspect, who was authorized to be on Naval Station Norfolk in Virginia and did not bring his own weapon on base, according to Capt. Robert Clark, the base's commanding officer.

The identities of the civilian and the sailor who were killed have not been released.

No other injuries were reported from the encounter, which occurred Monday about 11:20 p.m. on the USS Mahan, a guided-missile destroyer. It wasn't immediately clear why the civilian approached the ship or if he ever had access to it previously.

The shooting comes months after a September incident at the Washington Navy Yard, in which a gunman — identified as a contractor and former Navy reservist — killed 12 civilian workers before being shot to death.

The Navy said the civilian was coming toward the ship's quarterdeck, which is traditionally the ceremonial entry point aboard a ship, when the struggled ensued and the civilian was able to disarm the Petty Officer of the Watch.

Clark said the identification found with the civilian indicates it is unlikely he was a military dependent authorized to be on base for that reason. He said the civilian was found with a TWIC card. According to the Navy's Military Sealift Command, a TWIC card is a transportation worker's credential card and is necessary to apply for any jobs with the command.

Military Sealift Command hires civilian mariners to crew its ships, including the hospital ship USNS Comfort, which uses the same pier as the Mahan. Clark said it was unclear what exactly the civilian's job was or when he worked on the base.

The base was briefly on lockdown following the shooting, but traffic was back to normal early Tuesday morning.

The Navy will release both men's names after their families are notified, said Naval Station Norfolk spokeswoman Terri Davis.

Aside from the pier where the Mahan was docked, operations had returned to normal at the base, with counselors available, the Navy said in a statement.

But most enlisted sailors on the Mahan — docked at the first of 13 main piers — were not to report to duty Tuesday.

The shooting on the Mahan comes about a month after the Navy held anti-terrorism and force protection exercises on bases around the U.S., including an active-shooter drill at the Norfolk station.

To get on the base, civilians must be escorted or have identification that allows them to be there. Authorized civilians can include Department of Defense employees, contractors and military family members.

Each base entrance is guarded, and motorists present IDs. Inspections are rare. All 13 piers have additional security forces. As part of ongoing security efforts, handheld ID scanners were implemented this year at Navy bases in the region, including the Norfolk station.

The Norfolk base covers more than 6,000 acres and is the home port for 64 ships, according to information the Navy provided in February. About 46,000 military members and 21,000 civilian government employees and contractors are assigned to the base and its ships, according to the Navy figures.

The Mahan, commissioned in 1998, has a crew of nearly 300. In September, it returned to Norfolk after a deployment of more than eight months that included being positioned in the eastern Mediterranean Sea for a potential strike against Syria.

Clark became Naval Station Norfolk's commanding officer in February, after previously serving as the installation's executive officer since 2012.

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Associated Press writer Bernard McGhee in Atlanta contributed to this report.

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