A shooting spree by a 19-year-old Marine corporal on Monday has left four soldiers dead, the Marine Corps said.

The incident took place inside a barrack of the Marine Second Division on Ganghwa Island off the west coast at around 11:50 a.m., officials said. The corporal, identified only by his surname Kim, opened fire with a K-2 rifle.

Kim was captured after the incident.

A grenade also exploded at the scene, and its shrapnel apparently injured Kim, officials said, adding that they are now investigating how the incident took place.

A staff sergeant, two corporals and a lance corporal were killed in the rampage. Kim and another private first class who was injured in the incident are not in critical condition, officials said.

“We have set up an investigation team at the scene to find out the exact cause of the spree. We are sorry for causing concerns and will do our best to tighten military discipline, boost soldiers’ morale and prevent the repeat of such an incident,” Col. Kim Tae-eun told reporters.

The tragedy follows a set of incidents in the Marine Corps that have sparked criticism over “slackened discipline.”

On June 17, Marine troops fired at a South Korean passenger plane after mistaking it for a North Korean fighter jet. The troops from the Marine Second Division fired 99 shots with K-2 rifles at the Asiana flight carrying 119 crewmembers.

Marine officials said that the mistake was due to heavy fog. The incident resulted in calls for more enhanced education on how to distinguish between friendly and hostile aircraft.

On June 15, one Marine corporal stationed on Bangnyeong Island shot himself in the head with a K-2 rifle in an apparent suicide. The incident occurred while he was on a morning patrol mission.

By Song Sang-ho (sshluck@heraldcorp.com)