Seoul (AFP) - A South Korean soldier was sentenced to 45 years in military prison on Thursday for beating a conscript to death in a highly publicised case of barrack-room bullying.

At a court martial in Yongin City, south of Seoul, the defendant, a sergeant surnamed Lee, was convicted of instigating repeated beatings of a young private named Yoon.

"The accused committed a crime that amounts to outright murder," Yonhap news agency quoted the tribunal as saying.

Four other soldiers received jail terms of between 15 and 30 years and a sixth soldier was given a suspended prison sentence.

Private Yoon died on April 6 and investigators concluded death was caused by "crush syndrome" -- major trauma to the skeletal muscle -- and secondary shock from prolonged violence.

Prosecutors had sought the death sentence against Lee who led the others in subjecting Yoon to regular bullying and assaults, including sessions of crude water-boarding.

He was also humiliated by being forced to lick the spit of other soldiers from the ground.

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

Experts say the pressures facing 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, especially for those posted to the border with North Korea.

Bullying has been blamed for numerous suicides and incidents where conscripts have turned their weapons on their comrades.

In June, a 22-year-old sergeant opened fire on members of his unit in the 22nd Infantry Division, killing five and wounding seven.

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

Two army privates from the same division, also listed as mentally vulnerable, committed suicide later the same month.

The defence ministry in August said it would offer incentives and rewards for whistle-blowers who report any physical and verbal abuse in the barracks.

It also said it would toughen up penalties for those responsible and strengthen screening procedures to weave out draftees unfit for active or frontline duty.