SEOUL (AFP) - South Korean military prosecutors sought the death penalty Friday for a young conscript over last year's deadly shooting spree that killed five at a guard post near the tense border with North Korea.

At a court martial in the eastern city of Wonju, the prosecution said the 22-year-old sergeant surnamed Lim deserves death because he showed no repentance for his "premeditated and cruel" crime targeting unarmed comrades, according to Yonhap news agency.

In June last year, Lim hurled a grenade and opened fire on members of his own unit, killing five and wounding seven.

He was captured alive after he shot himself in the chest in a failed suicide attempt following a 24-hour standoff with thousands of troops.

Lim, who was listed as a soldier requiring special observation, told investigators he had been humiliated and constantly mocked.

Barrack-room bullying has long tainted South Korea's military service, and has been blamed for numerous suicides and incidents where conscripts have turned their weapons on their comrades.

Conscripts, most of them in their early twenties, account for the lion's share of the military's 690,000 active personnel.

In 2011 a 19-year-old marine conscript killed four colleagues on a western island near the border. Eight soldiers were killed in 2005 when a conscript threw a grenade and sprayed bullets over the sleeping men at a frontline guard post.

In both cases the men were court-martialed and sentenced to death, although the penalty was not carried out.

In October last year, an army sergeant was sentenced to 45 years in prison for beating a private to death, while four other soldiers received jail terms of up to 30 years.

Prosecutors said the private had been subjected to regular bullying and assaults, including sessions of crude water-boarding.