The president of the World Anti-Doping Agency (WADA) on Monday said his organisation had received "no credible evidence of wrongdoing" during their investigation into Chinese swimmers being allowed to compete after testing positive for a prescription heart drug.

The sport was rocked at the weekend by revelations that 23 Chinese swimmers tested positive for trimetazidine (TMZ) -- which can enhance performance -- ahead of the Tokyo Olympics in 2021.

They were allowed to compete after world governing bodies accepted China's findings that they had ingested it unwittingly from food during a meet in late 2020 and the early days of 2021.

"Having spoken at length with our science department, legal affairs department, legal affairs department and intelligence investigations unit, what I can say right now is that at every stage, WADA followed the whole due process and diligently investigated every line of inquiry in this matter," said WADA president Witold Banka.

"If we had to do it over again now, we would do exactly the same thing," he added.