Revelations of positive doping tests for nearly two dozen Chinese swimmers that went unpunished sparked an intense flurry of accusations and legal threats between the World Anti-Doping Agency and the head of the US drug-fighting organisation, who has long been one of WADA’s fiercest critics.

On Saturday, Wada it was turning to legal counsel to address a statement released by Travis Tygart, the CEO of the US Anti-Doping Agency, who said the world and anti-doping authorities in China swept positive tests “under the carpet by failing to fairly and evenly follow the global rules that apply to everyone else in the world”.

The allegation was made after Wada acknowledged it had cleared 23 Chinese swimmers who had tested positive for a banned heart medication to compete at the Tokyo Olympics in 2021 after agreeing with that country’s authorities that the samples had been contaminated.

Wada defended its process, and said it acted in good faith and according to due process when it decided not to challenge the Chinese explanation for the positives. It then turned its attention to Tygart, saying his comments were politically motivated and that it was “astonished by the outrageous, completely false and defamatory remarks” he made.

The global body pointed out that Usada had, several times over the years, accepted “similar conclusions of contamination involving a number of US athletes” and that Tygart “should realise that it is not only American athletes who can fall victim to situations of no-fault contamination”.

Tygart came back with another statement, noting the difference between his organisation’s handling of contamination cases and this one. The Chinese case involves a medication called trimetazidine (TMZ), the same drug taken by banned Russian figure skater Kamila Valieva before the Winter Olympics in Beijing in 2022.

A well-known prescription medication for people with heart disease, TMZ is known to help athletes improve stamina and decrease recovery times. Its use comes with the most stringent penalties under anti-doping rules.

Tygart said Usada’s previous contamination cases have not involved TMZ.

“And, most importantly, in all contamination cases that we have proven, we provisionally suspended the athlete, disqualified the results, found a violation, and issued an announcement as required by the rules,” he said.

None of that happened in the case of the Chinese swimmers, whose cases weren’t publicly revealed until reports by The New York Times and Daily Telegraph in Sydney surfaced on Saturday.

In explaining its handling of the case, Wada conceded there were difficulties in conducting investigations in China because of restrictions there because of Covid rules in place in early 2021 when the positive tests were uncovered. It said it consulted lawyers who advised that appealing the case was not warranted.

The disagreement is the latest chapter in years of sparring between Wada and Tygart, who has long felt it did not go tough enough on Russia after its government-sponsored doping scheme at the Sochi Olympics in 2014 was uncovered.

Another undercurrent of this case is the chance it could wind up in American court. Under a US law enacted in 2020 that was widely criticised by Wada, federal prosecutors can bring charges in doping cases that show a conspiracy to taint an international event involving US athletes.

“All of those with dirty hands in burying positive tests and suppressing the voices of courageous whistle-blowers must be held accountable to the fullest extent of the rules and law,” Tygart said.

But Wada was clearly thinking of different legal options when it shot back at Tygart.

“It should be noted that following Mr Tygart’s false allegations, Wada has no choice but to refer this matter to its legal counsel for further action,” the authority’s news release concluded, with the paragraph written in bold, black print.