South Korea's high military court has upheld a death sentence for a soldier convicted for killing five comrades in shooting and grenade attacks last year.

The assault was the latest in a series of shooting rampages by bullied soldiers in South Korea, which requires all able-bodied men to conduct about two years of military service in the face of a threat from North Korea.

The soldier, only identified by his surname Yim, told investigators he attacked his colleagues in June last year after seeing drawings they made of him that he considered insulting.

He was sentenced to death in February.

The Defense Ministry says the high military court on Monday rejected his appeal.

He can appeal again to the Supreme Court, a civilian court whose decision would be final.