Former USA Gymnastics team doctor Lawrence "Larry" Nassar, accused of molesting more than 100 female athletes over several decades, pleaded guilty Wednesday to multiple counts of criminal sexual conduct.

Nassar -- who was involved with USA Gymnastics for nearly three decades and worked with the country's gymnasts at four separate Olympic Games -- could be sentenced to at least 25 years in prison.

Nassar faced 22 criminal counts of sexual assault in Michigan for abusing athletes under the guise of providing medical treatment.

As part of a plea agreement, Nassar admitted to seven counts of abuse. Three of his victims were under 13 years old, and the others were aged between 13 and 15.

A handcuffed and gaunt Nassar appeared in court in an orange prison jumpsuit. Speaking softly and at times with heavy sighs, he pleaded guilty with a simple "yes" as each charge was read.

He then addressed the court with a statement.

He said he prayed for his victims and was "horribly sorry" for his crimes, which relate to events in Michigan that took place between 1998 and 2015.

"I want them to heal. I want this community to heal," Nassar said.

Judge Rosemarie Aquilina, addressing both Nassar and victims in the packed courtroom, said the former doctor's words "fall very short."

"You used that position of trust that you had in the most vile way -- to abuse children," Aquilina said.

"I agree that now is a time of healing. But, it may take them a lifetime of healing, while you spend your lifetime behind bars."

- A 'monster' -

Olympic gold medal-winning gymnasts Aly Raisman, McKayla Maroney and Gabby Douglas are among those who have said Nassar abused them.

Raisman reacted to the court hearing on Twitter, calling Nassar "a MONSTER not a doctor."

Rachael Denhollander, the first to publicly accuse Nassar, doubted his courtroom apology.

"He's a consummate narcissist. He's a master manipulator," Denhollander said at a post-hearing news conference.

"I don't believe there was anything sincere in what Larry said, other than his desire to refocus the attention on the good that he believed he did today."

The Michigan charges stemmed from Nassar's practice, based at Michigan State University, where prosecutors said 125 victims have come forward alleging abuse.

Prosecutors told the court all of the victims had approved of the plea agreement, under which eight charges were dropped.

- New 'safe sport policy' -

Nassar's case was part of a wide-ranging scandal which forced the resignation of USA Gymnastics chief Steve Penny in March.

Penny was accused by victims of failing to quickly notify authorities about abuse allegations.

USA Gymnastics adopted a new "safe sport policy" in response to the Nassar scandal that requires "mandatory reporting" of suspicions of sexual abuse.

With Nassar now being held accountable for his crimes, three of his victims and their lawyers demanded additional accountability from officials who were aware of prior accusations.

Denhollander accused the university, and the US Olympics and gymnastics organizations of being "unable to acknowledge" past failures.

"You have failed to hold anyone accountable for allowing a pedophile to flourish for decades," she said.

A civil lawsuit has been filed on behalf of about 100 of Nassar's alleged victims. Their attorney, John Manly, estimated that the total number could be as high as 160.

Manly accused Michigan State University of "stonewalling" his efforts to find out how university officials dealt with past allegations against Nassar, which had prompted a 2014 internal investigation.

In a statement, spokesman Jason Cody said the university "unequivocally" denied that it had "engaged in a 'cover up'," and pointed to a law enforcement probe earlier this year -- the results of which he said were shared with federal prosecutors.

"We have no reason to believe that any criminal conduct was found," he said.

Nassar has previously pleaded guilty to separate federal child pornography charges.

The judge in the state case set a January 12 sentencing hearing, during which victims will be given an opportunity to speak.

Nassar is also scheduled to appear in a separate plea hearing Monday on the remainder of the charges against him.