The World Anti-Doping Agency (WADA) is looking into new charges that four of Russia's gold-medal winners at the Sochi Olympics used steroids.

The latest allegations against Russian athletes were made by whistle-blower Vitaly Stepanov, a former Russian anti-doping official, in a CBS "60 Minutes" interview on May 8.

WADA spokesman Ben Nichols told the Associated Press on May 9 that the CBS program "revealed new and very disturbing allegations regarding Russian doping in sport. We will look into these without delay."

Russia won 13 gold medals at the Sochi Olympics. CBS did not reveal the names of the alleged drug cheats.

Previous allegations by Stepanov led to a WADA investigation that found systematic, state-sponsored doping in Russia's athletics program, and it was banned indefinitely from international competition.

Meanwhile, Russian sports officials dismissed the allegations.

"Stepanov is back on his hobby horse," Sports Minister Vitaly Mutko said.

The Russian Sports Ministry said it was "certain about the transparency of doping control" at Sochi, noting that its control stations employed "foreign experts."

"Furthermore," the ministry said, "a team of independent observers managed the doping control operations on a daily basis during the games."

Based on reporting by AP, AFP, TASS, and Reuters