A South Korean reservist has shot to death a fellow soldier and wounded at least three others before turning the gun on himself.

South Korean officials reported Wednesday that the man went on a shooting spree during a military drill in Seoul. The official said the reason for the shooting was not clear. The military is investigating.

South Korean men between the ages of 18 and 35 are required to serve two years of military service, under a system aimed at coping with security threats from neighboring North Korea. Following the mandatory service, the men must serve several more years in the reserves, undergoing regular training drills.

Reports say shooting incidents are not uncommon among South Korean servicemen on active duty but rare among reservists.