A whistleblower who uncovered systemic doping inside Russia's track team told "60 Minutes" he sent 200 emails and 50 letters about the cheating to the World Anti-Doping Agency, which told him it didn't have the power to investigate inside the country.

In an interview that aired on the CBS news show Sunday night, Vitaly Stepanov, a former worker at the Russian anti-doping agency, said after three years of correspondence, WADA eventually steered he and his wife, 800-metre runner Yulia, to a German TV network that produced the 2014 documentary that preceded WADA's investigation.

WADA spokesman Ben Nichols said before 2015, WADA didn't have authority to conduct its own investigations, and officials didn't think turning the information over to Russian investigators "would have led to the scrutiny required." Nichols said WADA was mostly worried that turning over the information would put the Stepanovs in danger.

As soon as the WADA code was revised in 2015 to give the agency power, "we acted without hesitation by forming the independent commission" that looked into the scandal, Nichols said.

Stepanov also told "60 Minutes" he's in contact with the former director of the Russian anti-doping lab, Grigory Rodchenkov, who told him a list of Russian athletes who used steroids at the Sochi Olympics includes four gold-medal winners.

Rodchenkov resigned his position in November, a day after WADA suspended his lab's accreditation. The WADA-appointed commission that looked into the Russian doping scandal said Rodchenkov, who is now living in an undisclosed location in the United States, was "at the heart" of the Russian doping conspiracy.

Russian Sports Minister Vitaly Mutko called Stepanov's allegations nothing more than speculation.

"Stepanov is back on his hobby horse," Mutko told Russia's state TASS news agency over the weekend.

In a separate statement Monday, the Russian sports ministry said it was "certain" about the transparency of doping controls during the Sochi Games.

"In addition to Russian specialists, doping control stations also employed foreign experts," the statement said. "Furthermore, a team of independent observers managed the doping control operations on a daily basis during the games."

The ministry said that, since the Stepanov's original statements last year, investigations have been carried out and Russia agreed on a road map with WADA to reform the doping control system.

Nichols said WADA officials watched the "60 Minutes" report, "which revealed new and very disturbing allegations regarding Russian doping in sport. We will look into these without delay."

The WADA-appointed independent commission made recommendations that led to the track team's suspension from international competition. That commission was not tasked with looking at other sports, though the commission chair, Dick Pound, wrote "there is no reason to believe that athletics is the only sport in Russia to have been affected by the identified systemic failures."

Several athletes have called for expanding the probe beyond track and field.

The latest news "is a clear call for WADA to embrace the athletes' demands for a broader investigation," Travis Tygart, the CEO of the U.S. Anti-Doping Agency, told The Associated Press.

WADA meets this week in Montreal, where it will discuss the independent commission's report. The track team's fate is expected to be decided next month by the sport's governing body.

In the "60 Minutes" story, Tygart called the new revelations about cheating in Sochi "clearly, the final nail in the coffin for Russian track and field."

Asked about his statement, Tygart told AP, "there's not enough time" for Russia to prove it is clean.

"They continue to attack the truth-tellers, denying the depth of the problem," Tygart said. "There's been no effective testing for months, no meaningful consequences. It just simply can't be done. It's not fair to clean athletes."