The head of the World Anti-Doping Agency said on Saturday that Russia's anti-doping authority was unlikely to be declared compliant with world sports rules before the Rio de Janeiro Olympic Games.

"As far as the Russian anti-doping agency is concerned, I think it highly unlikely that that organisation would be compliant by the time of the games in Rio," WADA President Craig Reedie told BBC radio in an interview on Saturday.

A report on Russia's compliance with doping rules would be sent to the International Olympic Committee which would then rule on whether the country's track and field athletes can take part in the Aug. 5-21 Games in Brazil, he said.

It would also be sent to the International Association of Athletics Federations which has to take a decision on whether to lift a suspension on Russia's track and field federation.

Allegations about systemic doping in Russian sport have been rumbling for months, but Moscow has been able to argue that the witnesses were unreliable and if there was wrongdoing, it was just a few isolated cases.

But comments by Grigory Rodchenkov, the former head of Russian sport's anti-doping laboratory, in what he described as an extensive programme to cheat at the Sochi Olympics takes the crisis over drugs in Russian sport to a new level of severity.

A Kremlin spokesman denied Rodchenkov's allegations, made in an interview with the New York Times, saying they amounted to "slander by a turncoat".

The chair of WADA's athletes committee said on Thursday that Russian athletes should be banned from the Rio Olympics unless there are guarantees that they are drug free.

Further allegations of drug use by Russian athletes appeared in U.S. media this week and Reedie told the BBC he was "horrified" by the claims, which have been denied by Russia.

"If these allegations are true, and they have to be investigated, then what has appeared to have happened is absolutely unacceptable and people can draw their own conclusions from those facts," he said.

Reedie also said he assumed a large percentage of the Russian team would be clean athletes.