The All Japan Judo Federation issued an apology Wednesday, admitting to allegations that 15 of its top female athletes were subjected to harassment and physical violence by head coach Ryuji Sonoda and other coaching staff.

“This is something that never should have happened,” said judo federation senior director Koshi Onozawa at a press conference held at the Kodokan in Tokyo’s Bunkyo Ward. “We will double efforts to make sure this never happens again.”

Sonoda, 39, and other coaching staff received an official warning in a letter in mid-January after being questioned by thejudo federation. The judo federation said it does not intend to release the names of the women or other coaches involved and at this juncture has no plan to replace Sonoda.

Asked by reporters if the public would find it acceptable to leave Sonoda in his current position as head coach given the circumstances, Onozawa only replied, “We want the public to closely watch his performance and let him demonstrate his achievements.”

The incidents involving Sonoda first came to light in September last year, and after wrestlers were questioned he was ordered to write an apology and given a strict reprimand in November.

Onozawa said he believed the incidents had been “settled” after Sonoda apologized directly to the wrestlers involved, but the group of 15 whistleblowers sent a written complaint to the Japanese Olympic Committee at the end of 2012.

The wrestlers complained in the document of being sworn at, slapped and hit with bamboo swords, while some were forced to compete in matches even though they were injured. That prompted them to ask the judo federation for an overhaul of the coaching staff, sources familiar with the matter said.

The judo federation said it has confirmed five cases occurred from August 2010 to February 2012, in which wrestlers were slapped, kicked or shoved.

The news comes on the heels of the suicide of a 17-year-old high school student in Osaka after he was physically punished by the school’s basketball club coach.

The education, culture, sports, science and technology ministry has ordered the JOC to conduct an investigation into incidents of violence in the judo federation.

Sports minister Hakubun Shimomura has said that if true the acts are “most deplorable.”