The United States Anti-Doping Agency (USADA) accused Russia of "hijacking" the Beijing Olympics on Monday following the decision to allow teenage skater Kamila Valieva to continue to compete despite a positive drugs case.

In a statement following the Court of Arbitration for Sport's ruling which allows Valieva to take part in individual events in Beijing, USADA expressed sympathy for the athlete at the centre of the controversy.

Chief executive Travis Tygart said "only time will tell" if Valieva should have been allowed to compete in Beijing after testing positive for the endurance-boosting angina medication trimetazidine.

But Tygart said if Valieva was later disqualified, the CAS ruling will "once again permit the Russians to taint the Olympic Games."

"Either way, for the sixth consecutive Olympic Games, Russia has hijacked the competition and stolen the moment from clean athletes and the public," Tygart said.

"If Russia would have properly processed this sample which they collected weeks prior to the Olympic Games, we would know for certain whether the women’s individual event starting tomorrow will be a real competition and whether she should have been allowed to skate in the Figure Skating Team Event."

The Valieva case has hinged on the delay between her sample -- provided at a competition in Russia on December 25 -- and its analysis, which was only carried out six weeks later.

Normally drug tests involving athletes preparing to compete in major championships would be expedited by the national anti-doping authority of the country involved.

But the World Anti-Doping Agency said the Russian Anti-Doping Agency (RUSADA) made no request to accelerate testing of Valieva's sample.

"If Russia had followed the rules, we would know for certain the outcome of the Figure Skating Team Event and those athletes who gave it their all could have their podium moment during these Games as they rightfully deserve," Tygart added.