USOC chief executive Scott Blackmun gave the deadline to the under-fire organisation in a letter sent to USA Gymnastics, according to CNN.

In the letter, Blackmun ordered the rest of the 21-member board to stand down as the fall-out to the sexual abuse scandal continues.

After former team doctor Larry Nassar was sentenced to 40 to 175 years in prison for seven counts of criminal sexual abuse against athletes including a host of Olympic champions and medallists, Blackmun had called on the USA Gymnastics board to quit in an open letter.

It was released amid mounting criticism of USA Gymnastics and the USOC for their failure to investigate claims of abuse raised by gymnasts.

Blackmun, who confirmed that an independent investigation would be launched, has seemingly gone a step further in the letter.

The USOC official said a "categorically fresh start at the board level" was required at USA Gymnastics and that an interim board should be put in place by February 28.

USA Gymnastics must then replace the interim directors within the next 12 months under the stringent set of requirements outlined by Blackmun.

Three board members - chairman Paul Parilla, vice-chairman Jay Binder and treasurer Bitsy Kelley - resigned earlier this week, while former President and chief executive Steve Penny quit in March amid pressure from the USOC.

The governing body must also cooperate fully with the independent investigation, launched "to examine how an abuse of this proportion could have gone undetected for so long".

Other criteria includes the complete implementation of recommendations made in an independent review of the organisation's methods, commissioned by USA Gymnastics and conducted by Deborah Daniels, a former federal prosecutor who spent a significant portion of her career prosecuting child sexual offenders.

"USA Gymnastics completely embraces the requirements outlined in the Jan. 25, 2017 letter from the USOC and appreciates the opportunity to work with the USOC to accomplish change for the betterment of our organisation, our athletes and our clubs," a statement from USA Gymnastics in response to the USOC read. 

"We understand that the requirements imposed by the letter will help us enhance our ability to build a culture of empowerment throughout the organisation, with an increased focus on athlete safety and well-being. 

"Our commitment is uncompromising, and we hope everything we do makes this very clear."

Nassar was sentenced after a week-long hearing in Lansing in Michigan, where 156 girls and women testified to being abused by the 54-year-old.

In handing down the jail term, Judge Rosemarie Aquilina said she had just signed Nassar's "death warrant".

Following the sentencing, International Gymnastics Federation (FIG) President Morinari Watanabe said he was "already profoundly shocked and saddened by the testimonies that many athletes have shared during the past year but the vibrant voices we heard in the courtroom these last days, telling of the sexual abuses they suffered, left my heart broken".

Japan's Watanabe also revealed an independent body, which would allow gymnasts to report any potential abuse, was in the process of being established.

The FIG have refused to comment on whether they will take any action against USA Gymnastics, however.

When asked by insidethegames, a spokesperson said they were "following the case with great attention".

Lou Anna Simon, the President of Michigan State University, has also resigned over the scandal.

The letter from Blackmun to USA Gymnastics can be read in full here.