Indianapolis, Indiana - America's 100m breaststroke world record-holder Lilly King called the latest doping scandal involving Chinese swimmers "disappointing and frustrating" as the sport gears up for its ultimate showcase at the Paris Olympics.

"It's extremely frustrating for the athletes to always have in the back of our mind that maybe this sport's not fair," King said on the eve of the US Olympic trials, which started Saturday in Indianapolis, Indiana.

"You know, when we put everything on the line, our privacy, really, everything that we do to compete with a level playing field, it's extremely frustrating to not have faith that others are doing the same thing."

King said it had been a "very interesting last couple weeks, months, and trying to focus on the meet but also kind of move forward with this.

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"But those thoughts are always in the back of my mind," she said.

The New York Times reported Friday that three Chinese swimmers who were among 23 involved in a drug scandal before the Tokyo Olympics had also tested positive for clenbuterol several years earlier.

The Times said the three athletes – including two 2021 Olympic gold medallists and a current world record holder – tested positive for the banned steroid in 2016 and 2017.

Chinese authorities argued the three athletes had ingested the substance inadvertently through contaminated meat, and no disciplinary action was taken – WADA defended that decision on Friday after the New York Times story was published.