SEOUL, May 13 (Yonhap) -- A reservist went on a shooting spree at a military training camp in Seoul on Wednesday, killing one person and wounding three others, before committing suicide, the Army said.

The 23-year-old reservist, identified only by his surname Choi," opened fire on his colleagues while receiving training at a military camp in Naegok-dong, southern Seoul, at 10:44 a.m. today," the Army said in a release.

Four reservists in their early and mid-20s who sustained injuries were rushed to nearby hospitals, but a 24-year-old later died and another is in critical condition, Army spokesman Ko Dong-heun said, adding that the shooter was found dead in an apparent suicide.

"After receiving a magazine with 10 rounds for a K-2 rifle, he fired one at the target before suddenly turning around to fire a total of seven rounds at other reservists," Ko said.

"He then aimed at himself and took his own life. Investigators are looking into what caused him to do so," he added.

Of 445 reservists who took part in the three-day training session from Tuesday, some 200 were participating in the shooting exercise, with exactly what happened before and during the training among the reservists yet to be known.

In South Korea, all able-bodied young men are subject to compulsory military service for about two years. Beginning in the following year after completing their active service, reservists are required to take part in an annual three-day training session up to six times in an eight-year period.

It is the first time in South Korea's military history that a reservist has opened fire on people, though the country has witnessed several suicides and accidents involving reservists with firearms.

While serving as an active-duty soldier, the shooter was on the military's list of draftees "requiring special attention," according to another Army officer. He refused to be identified.  

In a move to better manage the troops and to sort out the vulnerable, authorities made the list factoring in the results of enlistees' psychological consultations and their backgrounds.

"He had been transferred to several units during his service as he failed to adapt to the barracks life," he said, noting Choi was released from the military in 2013. "According to his medical records, he had received treatment for depression and showed signs of online addiction."

In June, an Army sergeant detonated a grenade and fired on his comrades at their front-line border outpost in Goseong, Gangwon Province, killing five and wounding seven others. He was also classified as a soldier requiring extra care.

This latest case sparked public ire over the military's lax management and control of trainings and weapons.

"Three captains and six other active-duty soldiers were at the scene, but none of them took action to prevent the casualties," another Army officer said. "A total of 20 lanes were there, and each was supposed to be controlled by one supervisor."

Expressing condolences to the victims and their bereaved family members, the defense ministry vowed to carry out a thorough probe and come up with measures to prevent a recurrence.

Meanwhile, South Korean rapper Psy had been at the camp to participate in the training prior to the incident, a source close to him said.

The "Gangnam Style" star "was granted an early leave due to an afternoon engagement," he said. "As the case occurred some 20 minutes after he left there, Psy had no idea there was such a case."