In a rare example of a victim going public with allegations in Japan, ex-soldier Rina Gonoi, 23, has said she was assaulted by multiple male colleagues during a training exercise last year.

The military acknowledged the assaults in September and apologised to Gonoi after she submitted a petition signed by more than 100,000 people demanding an investigation of her ordeal.

On Thursday, according to the Asahi Shimbun daily, four personnel in their 20s and 30s were dismissed, along with an officer in his 40s who allegedly gave them instructions.

Military authorities could not comment immediately when contacted by AFP.

Public broadcaster NHK reported that the head of the Ground Self-Defense Force, General Yoshihide Yoshida, said he felt "a strong responsibility as the leader of this organisation for causing sad and painful feelings" to Gonoi.

Gonoi said in a tweet on Thursday that she had filed a criminal complaint against three of the dismissed soldiers.

In September, the army acknowledged that Gonoi routinely faced sexual harassment and sexual assault at her unit and during training sessions.

On one occasion, a male colleague pressed on her neck, pushed her to the ground, forcibly spread her legs and repeatedly pressed his crotch against her. Two others then did the same.

Gonoi reported the incident to an army sexual harassment counsellor and the case was investigated and sent to prosecutors on suspicion of indecent assault.

But the case was dropped on grounds of insufficient evidence earlier this year.

Gonoi was recently chosen as one of the Financial Times' 25 most influential women of 2022.