The International Olympic Committee has reaffirmed its commitment to ensure a "good and robust" global anti-doping system as the US anti-doping agency's cover-up of drug violations is deepening fair competition concerns.

The United States Anti-Doping Agency has been embroiled in controversy due to an accusation that it allowed athletes to compete after testing positive for performance-enhancing drugs and worked undercover to glean information on other violators from 2011 to 2014. The practice was first reported by Reuters on Wednesday.

The World Anti-Doping Agency responded on the same day, saying that the tactic was not allowed and was against its global code. It also denounced the USADA's action of suspecting other countries' regulatory bodies while breaching international rules itself.

Asked about the scandal during a news conference on Thursday, IOC spokesman Mark Adams said, " Obviously, we're working with all of our stakeholders … to make sure that we have a good and robust world anti-doping system."

The revelation of the US tactic has raised more questions over the nation's handling of doping cases and undermined trust in its capability to preserve transparent and fair competition, Xinhua News Agency reported.

US sprinter Erriyon Knighton finished fourth in the men's 200-meter final at the Paris Olympics on Thursday. He tested positive for the banned substance trenbolone this year but was not suspended from the Games because the result was likely caused by contaminated meat.

As suspicions linger over his case, reporters rushed to the zone Knighton was required to pass through after the race and found no sign of him. His fellow teammates were seen speaking with reporters as usual.

"Knighton's silence is particularly striking given the ongoing scrutiny of doping practices. Questions remain as to why the typically outspoken Knighton has chosen not to address the media, leaving the doping controversy surrounding him unresolved in the public eye," Xinhua quoted an unnamed expert as saying.

Xinhua also reported on Friday that athletes, sports administrators and media outlets from multiple countries have questioned the antidoping work of the US following the Reuters report.

Questions have revolved around the nation's criteria for listing a drug on the banned substance list, the anti-doping testing regimens for the majority of US athletes in the professional leagues and college sports who do not compete under the global code, and the potentially negative impact of a US anti-doping law called the Rodchenkov Act that could disrupt the global harmonization of rules.

"The US' practice of allowing athletes who had doped to compete has threatened the integrity of sports competitions. Is it fair for other athletes on the stage?" said the Xinhua report.

China Global Television Network released the results of a survey involving nearly 15,000 netizens on Friday, showing that about 96 percent of global respondents believe the USADA has engaged in coverups and exonerated domestic athletes who were caught doping.

"As many as 96.23 percent of survey participants strongly demand increasing test frequency for US athletes so as to rebuild confidence in fair competition," said the survey.

Moreover, nearly 94 percent of respondents expressed concerns about whether doping tests at the 2028 Los Angeles Olympics can guarantee fairness and transparency, the survey added.