China's anti-doping agency (CHINADA) on Thursday urged the International Testing Agency (ITA) to intensify testing of U.S. track and field athletes, after American sprinter Erriyon Knighton tested positive for the banned substance trenbolone.

CHINADA accused the U.S. Anti-Doping Agency (USADA) earlier this week of double standards, saying its U.S. counterpart had been "trying its best" to clear U.S. athletes while accusing CHINADA and the World Anti-Doping Agency (WADA) of cover-ups.

Knighton tested positive for trenbolone this year but was not suspended for the Paris Games after an arbitrator found the result was likely caused by contaminated meat. The USADA chief has been outspoken about 23 Chinese swimmers who tested positive before the 2021 Tokyo Olympics but were allowed to compete.

CHINADA said on Thursday that trenbolone was a common contaminant in the United States, and athletes everywhere including U.S. athletes should pay close attention to meat contamination. Citing a recent WADA statement, it said that 31% of U.S. athletes were inadequately tested in the 12 months prior to the Tokyo Games.

"In light of the above, we strongly call on the International Testing Agency (ITA) to intensify testing on the U.S. track and field athletes," CHINADA said in a statement on its WeChat account.

"We also strongly recommend that the Athletics Integrity Unit (AIU) strengthen anti-doping supervision of the U.S. track and field, prevent the doping risks and strictly investigate relevant cases, in an endeavour to truly protect the legitimate rights and interests of the clean athletes around the world, and to rebuild the trust of global athletes in fair play."