South Korea's military on Tuesday announced tougher rules to combat barrack-room bullying after this month's deadly shooting rampage by a Marine who complained of abuse by superiors.

The defence ministry, in a new code of conduct, banned beating, other physical abuse, verbal insults, bullying and sexual harassment "under any circumstances".

It also bans troops who are not designated as commanders from giving orders to lower-ranking soldiers and warns that violators will face stern punishment, according to a ministry statement.

Those involved in beating and other physical abuse could face criminal charges in a military court, a defence ministry spokesman said, adding serious offenders may face a jail term of several years.

Less serious offenders could be demoted, take a salary cut or have their promotion prospects hampered, the spokesman told AFP.

There has been growing public criticism of the military's barrack-room bullying after the 19-year-old Marine corporal shot dead four colleagues and injured another.

The corporal surnamed Kim was himself injured by a grenade blast in a suicide attempt. He told military investigators he had been bullied by superiors.

The elite Marine Corps, responsible for guarding frontline islands near the tense border with North Korea, has also reported several recent suicides -- some of them apparently linked to bullying.

The defence ministry has vowed a crackdown on physical abuse throughout the 650,000-strong mainly conscript military.