The U.S. Anti-Doping Agency (USADA) has called for an overhaul of the World Anti-Doping Agency (WADA) and an independent investigation into Chinese swimmers testing positive before the Tokyo Olympics.

WADA has continued to rebut accusations from USADA chief Travis Tygart that the organization covered up the revelation that 23 Chinese swimmers tested positive for prescription heart drug trimetazidine (TMZ), which can enhance performance.

The USADA on Tuesday declared that no questions about WADA or China's anti-doping agency (CHINADA) were "satisfactorily answered" in WADA's news conference on Monday.