Four soldiers have been killed and one was injured when a corporal in South Korea's marine corps went on a shooting rampage on a Yellow Sea island base near the country's tense border with North Korea.
Defence officials said the corporal was taken into custody on Ganghwa Island, about 40 miles west of Seoul, but his motive remains unknown.
The man, whose surname is Kim, was also wounded but it was unclear whether he harmed himself or was hurt when he was apprehended, the officials said.
One of the killed soldiers was an officer, while the others were rank-and-file marines. The weapon used in the shooting could not be identified immediately, officials said.
The latest shooting is the worst to happen in South Korea's military since 2005, when a soldier threw a hand grenade and opened fire at a front-line army unit in a shooting rampage that left eight colleagues dead and several others injured.
Pfc Kim Dong-min later told investigators he went on that killing spree after being enraged by superiors who verbally assaulted him.
The shooting raised questions about the level of discipline in South Korea's 650,000-member military. All able-bodied South Korean men must serve about two years in the military under a conscription system aimed at deterring aggression from North Korea.
South Korea stations hundreds of marines on front-line islands within easy striking distance of North Korea. Last year, North Korea shelled a South Korean island, killing two civilians and two marines.
Boats routinely jostle for position in the waters - which are claimed by both countries - during crab-catching season, and three deadly naval clashes since 1999 have taken dozens of lives. The tension has taken its toll on South Korea's marines, who would take the brunt of any North Korean attack.
The South Korean military has beefed up marines' combat readiness on a cluster of bases in the Yellow Sea and increased high-tech weapons systems on the islands facing the North.