TOKYO (AFP) - Japan's navy has admitted a sailor killed himself onboard his ship after being persistently bullied by a superior, the latest incident to shed light on the country's little-discussed hazing culture.

Military police on Tuesday sent papers on the commanding officer to prosecutors, a naval spokesman said.

Maritime Self-Defence Force chiefs told reporters that Petty Officer First Class Koichi Goto, 42, was being investigated over claims that he persistently harassed his younger charge.

"It is deeply regrettable that the force could not prevent a suicide due to hazing," naval chief of staff Katsutoshi Kawano told a Monday press conference.

The crew member, reportedly in his 30s but whose identity is being withheld by his family, took his own life earlier this year after being repeatedly hit on the head by Goto and forced to kneel with his head on the ground, the spokesman said.

The sailor had frequently asked to be allowed time off, but Goto continued bullying him, he said.

The last time he had asked for leave, Goto made him stand in a hallway with a bucket, the spokesman said.

The crew man killed himself the following day, he added.

Goto has admitted he had exercised "excessive discipline" on his charge, the spokesman told AFP.

The case emerged months after the family of one serviceman was awarded US$700,000 (S$874,811) compensation after he took his own life. The 21-year-old killed himself in 2004 by jumping in front of a train after his senior officer reportedly shot at him with an airgun and forced him to buy pornographic movies.

Hazing is widely practised in many areas of Japanese life - in schools, workplaces and within sports - but is rarely reported unless it escalates into a suicide or a killing.

In 2007, a 17-year-old sumo apprentice died after a hazing incident involving his stable master and senior wrestlers. The stable master, who struck the teen with a beer bottle, was sentenced to five years' jail for negligence resulting in death.

The national women's judo coach quit in disgrace last year after 15 of his charges accused him and his staff of slapping, kicking and beating them during training in the run up to the London Olympics.

Observers say beating athletes with a bamboo sword was a nasty reminder of how Japan's sporting world still draws on the traditions that led the country to war last century.