(CNN) The US Olympic Committee's leader apologized Wednesday to all sexual abuse victims of former national gymnastics team physician Larry Nassar, saying the "Olympic family is among those that have failed you."
USOC Chief Executive Scott Blackmun also called on all USA Gymnastics board members to quit because of Nassar's abuse -- and threatened to decertify the sport's governing body if it doesn't agree to his demands.
Blackmun made the comments in an open letter published minutes after a Michigan judge sentenced Nassar on Wednesday afternoon to 40 to 175 years in prison.
"The purpose of this message is to tell all of Nassar's victims and survivors, directly, how incredibly sorry we are," wrote Blackmun, who became the committee's chief executive in 2010. "We have said it in other contexts, but we have not been direct enough with you. 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 said.
Blackmun also wrote that the USOC would look to decertify USA Gymnastics, which selects and trains US teams competing for Olympic and world championships in the sport, if it doesn't "fully embrace the necessary changes in their governance structure along with other mandated changes."
Three top USA Gymnastics board members resigned earlier this week -- a move Blackmun acknowledged but said wasn't enough.
"Further changes are necessary to help create a culture that fosters safe sport practice, offers athletes strong resources in education and reporting, and ensures the healing of the victims and survivors," Blackmun wrote.
"This includes a full turnover of leadership from the past, which means that all current USAG directors must resign," the letter said.
USA Gymnastics Chairman Paul Parilla, Vice Chairman Jay Binder and Treasurer Bitsy Kelley resigned Sunday. The Indianapolis-based governing body has 18 other board positions.
In a statement Wednesday night, USA Gymnastics said it supports Blackmun's letter and "accepts the absolute need of the Olympic family to promote a safe environment for all of our athletes."
It said it believes the interest of its athletes and the sport may be better served by "moving forward with meaningful change within our organization, rather than decertification."
USA Gymnastics also said it "supports an independent investigation that may shine light on how abuse of the proportion described so courageously by the survivors of Larry Nassar could have gone undetected for so long and embraces any necessary and appropriate changes."
Blackmun's letter also said:
• He is sorry that no one from the USOC was at Nassar's sentencing proceedings to hear victims' impact statements in person.
• The committee will launch "an investigation by an independent third party" to determine when complaints against Nassar were reported, who received the complaints and why the abuse went on "for so long."
• The USOC will devote "substantial funds" to give abuse survivors access to treatment and counseling -- details of which are to be announced "soon."
Nassar pleaded guilty to seven counts of criminal sexual conduct and admitted to using his trusted medical position to assault and molest girls under the guise of medical treatment. In wrenching victim impact statements over the past two weeks, more than 150 women and girls said in court that Nassar sexually abused them over two decades.
USA Gymnastics counted Nassar as part of its medical staff or as national team doctor through four Olympic cycles. Nassar also was a sports physician at Michigan State University from 1997 to 2016.
All three entities -- the USOC, USA Gymnastics and Michigan State -- have been accused by some victims and their representatives of failing to protect them.
USA Gymnastics and Michigan State have separately said they reported Nassar's abuse immediately when they learned about it, but a number of victims said they told authorities about the abuse years ago and were ignored.
John Manly, an attorney who represents more than 100 women in civil lawsuits relating to the Nassar case, earlier this week called on Congress to hold hearings and investigate the USOC, Michigan State and USA Gymnastics in connection with the abuse scandal.
"Many of the Board Members who remain were well aware of USAG's concealment of sexual abuse, its noncompliance with reporting statutes and harsh treatment of sexual abuse survivors," Manly said in a statement.
"In order for the sport to survive, the entire Board and Officers of USAG needs to be reconstituted. If that does not happen, the United States Olympic Committee should decertify the organization and charter a new organization run by people that will put the safety of children and athletes ahead of money and medals."