The whistleblower alleging state-sponsored drug cheating by Russia has said on US television that he has tapes of the former head of a drug testing laboratory telling him that at least four Russian gold medallists at the 2014 Winter Olympics in Sochi were using steroids.
Vitaly Stepanov, who previously worked for Russia's anti-doping agency and is now living in the United States, says Grigory Rodchenkov informed him in over 15 hours of taped conversations he had evidence of a Sochi Games testing cover-up, which included the use of Russian intelligence agents.
Stepanov said Rodchenkov told him "that FSB agents worked as doping controls officers during the Sochi Games, that FSB tried to control every single step of the anti-doping process in Sochi."
FSB refers to Russia's Federal Security Service.
The American 60 Minutes program said it had listened to all 15 hours of tape and that at one point, Rodchenkov told Stepanov he was in possession of what he called "the Sochi list" of four Russian gold medal winners who were doping.
World Anti-Doping Agency spokesman Ben Nichols said the allegations about use of Russian intelligence in a doping cover-up and that four gold Sochi gold medallists were doping were "very disturbing".
"WADA has watched the CBS 60 Minutes program, which revealed new and very disturbing allegations regarding Russian doping in sport. We will look into these without delay," Nichols said.
Russia is already banned from all track and field competitions, including August's Rio Olympics, after an independent WADA commission last November revealed widespread state-sponsored doping.