Rachel Axon, Roxanna Scott and Nancy Armour

USA TODAY Sports

Corrections & clarifications: A previous version of this story misstated the date that Maroney tweeted. She tweeted Wednesday morning.

Olympic gold medalist McKayla Maroney said former USA Gymnastics doctor Larry Nassar sexually abused her over several years, beginning at the age of 13 when she was invited to a national team training camp.

Maroney wrote on Twitter that Nassar, who has been accused of assaulting at least 140 girls and women, abused her under the guise of medical treatment. He is on trial in Michigan facing sexual assault charges and awaits sentencing on federal charges.

The abuse continued until she left the sport, Maroney said. "It seemed whenever and wherever this man could find the chance, I was 'treated.'"

Brennan:Maroney gives courageous voice to sexual abuse

Related:Judge refuses to delay sex assault trial for Larry Nassar

More:Aly Raisman criticizes USA Gymnastics, USOC for response to sex abuse

More:Timeline: Former USA Gymnastics doctor Larry Nassar

The 21-year-old from Long Beach, Calif., said she was abused before her U.S. team won gold at the 2012 London Olympics and before she won silver on the vault.

"We are sickened that some of the abuse committed by Nasser may have occurred during the 2012 Olympic Games, and heartbroken that McKayla was one of his victims," U.S. Olympic Committee spokesman Mark Jones said.

Maroney also described an incident that she said occurred at the 2011 world championships in Tokyo, when she was 15. She said Nassar had given her a sleeping pill "and the next thing I know I was all alone with him in his hotel room getting a 'treatment.' I thought I was going to die that night."

She posted the tweet describing the abuse early Wednesday morning with the #MeToo hashtag.

"People should know that this is not just happening in Hollywood," Maroney wrote. "This is happening everywhere. Wherever there is a position of power, there seems to be potential for abuse. I had a dream to go to the Olympics, and the things that I had to endure to get there were unnecessary and disgusting."'

Maroney dreamed of becoming an Olympian while watching the 2004 Olympics. "From the outside looking in, it's an amazing story. I did it. I got there, but not without a price," she wrote.

In July, Nassar pleaded guilty to federal child pornography charges, and faces 22 to 27 years in prison when he’s sentenced Dec. 7. He still faces 33 charges of criminal sexual conduct in Michigan.

Nassar was the USA Gymnastics team physician for nearly 20 years and worked with gymnasts at four Olympic Games. USA Gymnastics fired him after receiving a complaint in the summer 2015, but waited five weeks before alerting the FBI.

The abuse did not become public until two former gymnasts told The Indianapolis Star last year that they were abused by Nassar during the 1990s and early 2000s. They said he molested them during multiple treatments. The Indianapolis Star is part of the USA TODAY NETWORK.

According to the Lansing State Journal, also part of the USA TODAY NETWORK, more than 140 women and girls have since said Nassar sexually abused them, with nearly all of them saying it happened during medical appointments.

The abuse scandal led to the ouster of USA Gymnastics CEO Steve Penny, who resigned in March under pressure from the U.S. Olympic Committee. USA Gymnastics has not hired his replacement.

It also prompted a far-reaching review of the federation’s practices by former federal prosecutor Deborah Daniels. In her report, Daniels said USA Gymnastics needed a “complete cultural change” so the safety and well-being of athletes is the priority rather than world and Olympic medals.

"USA Gymnastics admires the courage of those, like McKayla Maroney, who have come forward to share their personal experiences with sexual abuse. Because of their strength in coming forward, predators can be held accountable for their actions," USA Gymnastics said in a statement. "We, like so many others, are outraged and disgusted by the conduct of which Larry Nassar is accused. We are sorry that any athlete has been harmed during her or his gymnastics career.

"We are strengthening and enhancing our policies and procedures regarding abuse, as well as expanding our educational efforts to increase awareness of signs to watch for and reporting suspicions of abuse, including the obligation to immediately report."

Aly Raisman, captain of the past two Olympic teams and Maroney’s teammate in London, has criticized USA Gymnastics and the USOC for their response to the sexual abuse crisis. During the national championships in August, she said she feels the governing body is more concerned about sweeping the abuse cases under the rug or protecting themselves legally than making sure it never happens again.

The Indianapolis Star has reported more than 360 cases in which gymnasts have accused coaches of sexual transgressions over 20 years.

“The people at the very top, that work at the office every single day at USA Gymnastics, they need to do better,” Raisman said.

USA Gymnastics has adopted all 70 recommendations made by Daniels and is in the process of implementing them. Some have already been addressed with the opening of the U.S. Center for Safe Sport, an independent agency created by the USOC to handle sexual misconduct cases in the Olympic movement.

"We’re grateful to McKayla and the many other athletes who have spoken out and added their voices to making sure this doesn’t happen again," Jones said.