The US Anti-Doping Agency (USADA) on Wednesday called for an independent investigation into the case of 23 Chinese swimmers who failed doping tests ahead of the Tokyo 2021 Olympics.
The World Anti-Doping Agency (WADA) published a "frequently asked questions" document outlining its handling of the case on April 29, following wide-ranging outrage after news of the case broke.
However, USADA said WADA was "doubling down on half-truths and self-serving rationalizations" in the document.
"How much longer must we watch WADA dance around the truth, avoiding all accountability and responsibility?" USADA said.
"We echo athletes' demands to create a truly independent investigation and let impartial experts and stakeholders participate in the process," the US body said.
"We must get real answers, ensure accountability for any failures, and secure true reform at WADA to fulfill the promise we all have to clean athletes and the fairness of sport."
The swimmers tested positive for the banned heart medication trimetazidine (TMZ) at a domestic competition in Shijiazhuang in early 2021. Chinese officials said the swimmers tested positive due to contamination and reported the case to WADA and the swimming governing body World Aquatics (then FINA).
WADA confirmed the positive tests, but like FINA said it found no credible evidence of misconduct in its own review.
A 30-strong Chinese team, including 13 of the 23 with positive tests according to reports, went on to win six medals in Tokyo, including three gold medals.
Failing to publicly announce the case in the weeks before the Olympic Games could only be described "as WADA covering up those cases," USADA said.
"Indeed, these cases would remain covered up by WADA had it not been for brave whistleblowers and reporters who rightfully brought these cases to light. WADA needs to be held to account."