SEOUL –

A soldier in South Korea's reserves went on a shooting spree Wednesday, killing a fellow soldier and injuring three comrades before shooting himself dead, a military official said.

The incident will spur questions over the country's rules on compulsory military service at a time when its military faces criticism of lax discipline in some units, leading to attacks on soldiers by colleagues suffering from psychological problems.

The military official said the reservist turned his K-2 assault rifle on fellow soldiers during mandatory training at a reserve forces site in the capital, Seoul. He was 24, said South Korean cable television network YTN.

"The army is investigating the incident," said the military official, who declined to be identified because the topic is sensitive.

South Korea has a system of two years of compulsory military service for all able-bodied men, since it is still technically at war with North Korea after the 1950-53 war between the neighbors ended in a truce and not a peace treaty.

They must then participate in annual military training as reservists for eight years.

South Korea's military has about 630,000 soldiers on active duty, more than 300,000 of them conscripts, aimed at deterring aggression from North Korea, one of the world's most militarized states.

But the country's declining birthrate and small families have prompted concerns its armed forces have become too slow to deal with social changes.

Rights group Amnesty International on Wednesday urged South Korea to end the imprisonment of hundreds of young men who object to military service on grounds of conscience.

The most recent outcry concerned continuing physical and emotional abuse that led to the death of a conscript at the hands of his barrack mates last year.

Last year a conscript soldier threw a grenade and shot dead five comrades near the border with North Korea.