Russian doctors and athletes worked together to evade drug tests at the Sochi Olympics, passing containers of urine through a hole in the wall to replace tainted samples, The New York Times reported Thursday.
Grigory Rodchenkov, the former head of Russia's national anti-doping laboratory, is quoted by the newspaper as saying he replaced samples with clean urine at night through a hole in the wall at the laboratory in Sochi during the 2014 Winter Games.
The International Olympic Committee called Thursday's report "very worrying,'' saying Olympic officials would work with the World Anti-Doping Agency to investigate.
WADA president Sir Craig Reedie promised to make inquiries about detailed allegations.
"We understand fully that, in the current climate, with new doping allegations surfacing, we have work to do to further secure athletes' confidence in clean sport," Reedie said. "We appreciate the sense of urgency in light of the upcoming Rio Games and I can assure you that we take this responsibility very seriously."
Rodchenkov told the newspaper a man he believed to be from Russia's Federal Security Service arrived at his lab in Moscow in late 2013 inquiring about the supposedly tamper-proof bottles used to store urine samples.
He figured out a system to replace the bottle caps, then delivered clean urine -- in soda or baby bottles -- that had been collected from the athletes before the Olympics.
Athletes took photographs of their drug forms so the samples could be identified later and switched, according to The Times.
The operation worked "like a Swiss watch,'' Rodchenkov told the newspaper.
Rodchenkov is calling on Olympic officials to test stored samples with his assistance. He and the filmmaker he is working with on a documentary sent a letter, obtained by The Associated Press on Thursday, to the presidents of the IOC and WADA, urging them to test the samples while the videographer films the action.
At least 15 medal winners in Sochi, including fourteen members of Russia's star cross-country ski team and two veteran bobsledders who captured two gold medals, were listed on a spreadsheet of athletes provided by Rodchenkov, the newspaper reported.
Rodchenkov talked to the newspaper in interviews arranged by filmmaker Bryan Fogel, who is working on a documentary about doping.
Sports Minister Vitaly Mutko defended the Russian athletes.
"They are outstanding athletes, and the accusations are absurd,'' Mutko told the state Tass news agency. "The accusations against them are absolutely groundless. We will study this article and will decide how to react.''
Calls to two numbers for Rodchenkov were not answered Thursday.
Two former executives from the Russian national anti-doping agency, Nikita Kamayev and Vyacheslav Sinev, died within the space of two weeks in February. The agency said the 52-year-old Kamayev had died of a heart attack after skiing, and did not elaborate on the cause of death for Sinev, 58. The agency had been accused by WADA in November of covering up doping.
On Wednesday, Mutko had told Tass that Russian sports were under an "information attack'' from Western media, without explicitly referring to a specific story. "Actually there is nothing to back all of this up. No facts,'' he said.
Russia's track team is currently banned from international competition over doping allegations, and the sport's governing body will decide next month whether the team should be allowed to compete in Rio.
The number of anti-doping tests conducted in Russia has dropped by nearly two-thirds since the country's drug-fighting agency was suspended and placed under new management.
WADA officials released the figures Thursday. They said there were 2,244 tests on Russian athletes from Nov. 18 through May 5, compared to 6,890 tests during the same period the previous year.
The British anti-doping agency, with help from international advisers, is trying to rehabilitate Russia's program but has run into several obstacles.
WADA said the British agency was able to find only 10 doping-control officers to collect samples throughout the vast country. And some of those officers, when trying to enter Russia's military bases, were turned away and threatened with having their visas revoked if they returned.
The Associated Press contributed to this report.