An Army private shot himself dead with his assault rifle early this week while on duty at a frontline unit, the latest in a recent string of deaths of conscripts, officials said Thursday.

The private, identified only by his surname Choi, was found dead with a bullet in his head in the pre-dawn hours of Monday outside a military post near Hwacheon, 118 kilometers northeast of Seoul, according to the Army. A suicide note was found on the scene.

A senior soldier who was on duty with Choi at the guard post found the body of the private outside the post after hearing sounds of gunfire, military authorities said.

The suicide note indicated Choi had been under severe pressure during his service and endured tougher discipline in his unit.

"My fatigue doesn't go away despite much sleep. I have become more and more forgetful. I realize I am such a fool," the note read.

An official said the Army is investigating to determine the exact cause of Choi's suicide and whether he had been harassed prior to his death.

The military has been under growing criticism for a spate of deaths of conscripts.

Last month, a 23-year-old recruit died of inflammation of the brain and meninges, the membranes that cover the brain and spinal cord, two days after he showed a sudden high fever following a 20-kilometer endurance march.

Military investigators said inappropriate medical treatment is believed to be partly to blame for the death of the recruit.

All-able bodied South Korean men are required to serve at least two years for the military, which faces North Korea across the heavily fortified border. (Yonhap News)