BEIJING - The World Anti-Doping Agency told Agence France-Presse on Wednesday that it will not appeal against a three-month ban imposed on Chinese Olympic champion swimmer Sun Yang.

WADA had considered action after Sun tested positive for the stimulant trimetazidine in May and was banned for three months by the China Anti-Doping Agency (CHINAD) Abut it was only announced in November after the Asian Games.

The swimmer insisted that he did not know the substance was banned, and that he took it to cure heart palpitations.

"WADA has reviewed the full case file for the Chinese swimmer Sun Yang and has decided not to appeal the decision by the Chinese Swimming Federation to impose a three month sanction," WADA spokesman Ben Nichols told AFP in a statement.

"WADA has written to CHINADA however, raising its concern over the delayed public reporting of the case," the spokesman added.