Rina Gonoi, 23, went public about the alleged assaults last year, after an investigation into her claims was dropped on the grounds of insufficient evidence.

Friday's move by the prosecutors in Fukushima region, where Gonoi was previously stationed, is a reversal of their initial conclusion not to prosecute.

A spokesman for the prosecutors' office told AFP they could not confirm the decision over the phone.

"Today, the three were charged over sexual assault against me... I finally feel (my efforts) paid off because every day I was suffering," Gonoi wrote on Twitter.

"I want them to acknowledge what they did is a crime and atone for their sin."

Last month, Gonoi told AFP in an interview that on a drill in 2021, three colleagues pressed her to the ground, forced apart her legs and each repeatedly pressed their crotches against her.

She reported the incident, but an internal probe concluded there was not enough evidence to proceed.

After Gonoi aired her claims in a video posted on YouTube last June, more than 100,000 people signed a petition and she submitted it to the defence ministry seeking an independent probe.

The defence ministry has since acknowledged the assault and apologised.

For Gonoi, who had dreamed of joining Japan's Self-Defense Forces from childhood, the decision to publicly call out the inaction surrounding her assault was agonising.

"It was the last resort," she told AFP, describing herself as "desperate rather than brave".

The ex-soldier is also suing the government and her perpetrators over the "superficial" apologies and mistreatment she received.