A South Korean female naval officer apparently killed herself after being allegedly raped by a senior colleague, a defence ministry spokesman said Thursday.

The victim, a lieutenant, was found dead in her single-room apartment on Wednesday, where a message was found reading: "Tomorrow, I won't be in this world any longer."

"The lieutenant appeared to have committed suicide," a military spokesman told AFP.

She had reportedly told her boyfriend that she had been raped.

Military police have arrested a navy captain as a suspect. He admitted to having sex with her but denied the rape allegation, the spokesman said.

Human rights activists say cases of sexual violence within the military occur persistently despite government efforts to curb them.

"This appears to be a typical case in which a male superior abused his power to violate a female subordinate," Bang Hye-Lim at the Military Human Rights Centre told AFP.

"It is not rare at all that male chauvinism translates into sex crimes in the military", she said.

A parliamentary probe revealed last year that a total of 111 female soldiers had fallen victim to rape by their seniors over the previous five years.

The latest alleged incident emerged a day after a South Korean army officer was sentenced to six months in prison for having consensual gay sex with a colleague.