PYEONGCHANG, South Korea (Reuters) - The U.S. Olympic system “failed” the hundreds of young female athletes sexually abused by former USA Gymnastics doctor Larry Nassar, United States Olympic Committee (USOC) Board of Directors Chairman Larry Probst said on Friday.

He also said the USOC had not taken steps quickly enough to contact gymnasts abused by Nassar and that it had erred by failing to attend earlier sentencing hearings.

Olympic champion Simone Biles is among several gymnasts who have criticized USOC for not making efforts to get in touch with them as the scandal unfolded.

UltraViolet Action, a women’s advocacy group in the United States, on Friday called for USOC Chief Executive Scott Blackmun to resign for failing to adequately respond to reports of Nassar’s abuse before he was criminally charged.

A letter by the women’s group signed by sexual abuse survivors says, “It’s unconscionable and unacceptable that no one has been held accountable at the USOC.”

Dozens of the victims have accused officials at the USOC, USA Gymnastics and Michigan State University of failing to investigate complaints stretching back decades.

The board of directors of USA Gymnastics stepped down after U.S. Olympic officials threatened to decertify the governing body.