LOS ANGELES (AFP) - The United States Olympic Committee announced an independent inquiry into the US gymnastics sex abuse scandal on Wednesday (Jan 24) and called on the sport's entire board of directors to resign.

In an open letter released as disgraced USA team doctor Larry Nassar was sentenced to up to 175 years in prison, USOC chief executive Scott Blackmun said the third party investigation would seek to establish "who knew what and when".

"The USOC has decided to launch an investigation by an independent third party to examine how an abuse of this proportion could have gone undetected for so long," Blackmun wrote.

Both USA Gymnastics and USOC would be investigated, Blackmun added. Both organisations have been accused of failing to act swiftly when allegations against Nassar first emerged.

"We need to know when complaints were brought forward and to who," Blackmun said. "This investigation will include both USAG and the USOC, and we believe USAG will cooperate fully."

Three top officials of USA Gymnastics' board of directors resigned last weekend but USOC is demanding an entire overhaul of the board.

"Further changes are necessary to help create a culture that fosters safe sport practice... this includes a full turnover of leadership from the past, which means that all current USAG directors must resign," Blackmun said.

More than 150 of Nassar's victims gave statements at his sentencing hearing in Michigan. The doctor's victims included several high-profile stars including Olympic gold medallists Simone Biles, Aly Raisman, Gabby Douglas and McKayla Maroney.

'OLYMPIC FAMILY FAILED YOU'

Blackmun apologised for USOC's failure to attend the sentencing hearing, which he said had "framed the tragedy through the eyes of the victims and was worse than our own worst fears".

"The USOC should have been there to hear it in person, and I am deeply sorry that did not happen," Blackmun said, adding that his letter was intended as an apology to Nassar's victims.

"We are sorry for the pain caused by this terrible man, and sorry that you weren't afforded a safe opportunity to pursue your sports dreams. The Olympic family is among those that have failed you," he wrote.

Blackmun said USOC had considered disbanding USA Gymnastics but ultimately had decided to allow the sport's governing body to continue.

"We have strongly considered decertifying USAG as a National Governing Body," he wrote.

"But USA Gymnastics includes clubs and athletes who had no hand in this and who need to be supported.

"We believe it would hurt more than help the athletes and their sport. But we will pursue decertification if USA Gymnastics does not fully embrace the necessary changes in their governance structure along with other mandated changes under review right now."

USA Gymnastics president and chief executive Kerry Perry, who took over the organisation last December, said she was determined to reform the body.

"The powerful voices and strength of these survivors have left a lasting impression on all of us," Perry said.

"Every day, their stories will impact my decisions as president and CEO ... I will not waiver on my commitment to focus each and every day on our organization's highest priority - the safety, health and well-being of our athletes."