South Korean Defence Minister Han Min-Koo apologised Monday and the presidential Blue House urged a full inquiry following the death of a bullied young army conscript.

"I extend my sincere apology," Han told parliament, describing the death of the 23-year-old private as "an incident that should not happen in a civilised society in the 21st century".

Five soldiers have been arrested on manslaughter charges after an initial investigation showed the private, surnamed Yoon, had been repeatedly bullied.

The five were allegedly involved in an assault on Yoon in April, during which he was struck in the chest, causing a chunk of food to get lodged in his airway. He died of asphyxiation.

The case came on the back of two separate suicides by army privates last month, and a deadly shooting spree in June in which a sergeant killed five members of his unit for taunting him.

Investigators found Yoon had been the target of regular bullying and assaults, including sessions of crude water-boarding.

He had also been forced to eat a tube of toothpaste and lick the spit of other soldiers from the ground. Investigators are also looking into allegations he was sexually molested.

President Park Geun-Hye's office called for a thorough investigation as public concern grew over barrack-room bullying.

"Priority must be put on ensuring a similar incident will not happen again," presidential spokesman Min Kyung-Wook told reporters.

Bullying has long tainted South Korea's military service, which is mandatory for all able-bodied men between the ages of 18 and 35.

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

Experts say the pressures facing the young servicemen can be daunting when, after what is often quite a cosseted childhood and teenaged youth, they are suddenly plunged into a world of harsh military discipline.