A South Korean reserve soldier went on a shooting spree Wednesday, killing a fellow reservist and injuring three others before killing himself, army officials said.

The soldier opened fire with a K-2 rifle on fellow reservists during mandatory drills at a reserve forces training site in Seoul, the army officials said speaking on condition of anonymity because of office rules.

The soldier committed suicide after the rampage and one of the injured was declared dead at a hospital, the army officials said.  The military is investigating but had no other initial details, they said.

Shootings at military barracks by soldiers have happened with some frequency in recent years, raising worries about bullying and mental health conditions in the country's armed forces. But a shooting spree involving a reservist is unusual.

Last year, a South Korean soldier threw a grenade and opened fire on colleagues, killing five and wounding seven others. He later told investigators he shot fellow soldiers after seeing a drawing they made of him that he considered insulting.

All able-bodied South Korean men must serve about two years of mandatory military service under a conscription system aimed at coping with threats from rival North Korea. Past rampages raised questions about the discipline and readiness of the South Korean military.

After finishing their military duties, South Korean men are required to take annual military training as members of the country's reserve force for eight years and their training involves shooting drills for the first six years, according to the Military Manpower Administration.