The World Anti-Doping Agency (WADA) said Tuesday it was investigating fresh claims of Russian doping involving four Sochi 2014 Winter Olympics gold medallists.
The allegations - the latest in a slew of doping accusations to rock Russian sport -- were made by whistleblower Vitaly Stepanov in an interview aired on Sunday by American channel CBS.
While Russia have dismissed the claims as an attempt to derail upcoming WADA talks, the anti-doping agency expressed its concern.
"WADA will probe these new allegations immediately," WADA President Craig Reedie said in a statement.
"The claims made in the program offer real cause for concern, as they contain new allegations regarding attempts to subvert the anti-doping process at the Sochi Games."
Russia won 13 gold medals at the Sochi Winter Olympics. The names of the alleged drug cheats were not revealed in the CBS programme.
WADA will host meetings of its executive committee and its foundation board in Montreal later this week where they are expected to discuss doping in Russian sport, among other topics.
A WADA independent committee concluded in a report published in November there was evidence of "state-sponsored" doping and mass corruption in Russian athletics.
The International Association of Athletics Federations suspended Russia over the report, with the IAAF council due to decide in June if the country's athletes can compete at the Rio Olympics.
In Sunday's interview Stepanov - a former Russian Anti-Doping Agency (RUSADA) official - cites Grigory Rodchenkov, former head of Russia's now-discredited drug testing lab, as telling him that FSB state security service officers "tried to control every single step of the anti-doping process in Sochi".
WADA chief Reedie said: "Mr. Rodchenkov was of course interviewed by WADA's Independent Commission that exposed widespread doping in Russian athletics last year.
"Yet, regrettably, he was not forthcoming with such information related to the Sochi Games. It is surprising to hear these views so many months after the Commission concluded its work."
A statement published Monday by the Russian sports ministry said that Moscow was "certain about the transparency of doping control during the Olympic Games".
And on Tuesday Natalia Jelanova an advisor to the Russian sports ministry, said: "We are worried of course over Stepanov's comments, although he has no link with (Russian) anti-doping bodies."
She added in an interview with R-Sport that russia was ready to provide WADA with any dcouments they requested.
Reedie meanwhile highlighted the part played by Stepanov and his wife, banned 800-metre runner Yuliya Stepanova, in laying bare the extent of doping in Russia.
"There is no question that the Stepanovs provided vital information and intelligence that allowed the Commission to be established; and, without which, widespread doping in Russian athletics may never have truly been exposed."
Updated Date: May 10, 2016 22:38 PM