Russian President Vladimir Putin's spokesman on Friday rejected claims that a former senior sports official participated in a state doping programme during the 2014 Winter Olympics in Sochi as a "defector's slander."
Spokesman Dmitry Peskov says in comments carried by state news agency TASS that the accusations which included 15 doped medal winners are "not based on any reliable information."
In an interview with The New York Times published Thursday, Grigory Rodchenkov, a former director of a laboratory that tested Russian athletes for performance-enhancing drugs, said he helped provide such drugs to athletes and switch out drug-tainted testing samples with clean ones.
The World Anti-Doping Agency (WADA) said it will investigate the latest allegations while a German Olympic official called for harshest sanctions and the French athletics chief proposed to ban the whole Russian team from the upcoming Rio de Janeiro Olympics - if the allegations are true.
The Russian athletics team is already suspended after a report from a WADA commission, and it remains unclear whether they will be able to compete.
The allegations, along with a recommendation by the WADA foundation board to declare distance-running powerhouse Kenya non-compliant, and a French probe into payments around the election of the 2020 Games host city are casting a dark shadow over the Olympics 12 weeks ahead of opening ceremony in Rio.
The New York Times article was published during Thursday's WADA meeting, with the paper quoting Rodchenkov as saying Russian athletes submitted clean urine samples ahead of the Sochi Games which where then used to replace tainted samples taken during the Olympics, via a hole in the wall of the laboratory.
The scheme reportedly involved athletes, officials and the secret service, and Rodchenkov told the New York Times it worked "like a Swiss watch."
He said he made a cocktail of three forbidden substances which Russian athletes used to boost their performance.
Russia topped the Sochi medal table with 33 medals, 13 of them gold.
"You can be sure that WADA will immediately look into these additional allegations," WADA president Craig Reedie said in a statement Thursday.
The International Olympic Committee (IOC) has also asked WADA to investigate, and Rodchenkov has written to the IOC and WADA offering to provide information.
"We would of course welcome any evidence that will help to determine the truth or otherwise of these allegations," the IOC said.
"If any wrong doing is uncovered the IOC will not hesitate to act decisively to punish those responsible and to defend the clean athletes."
The latest reports have further tainted Russia's reputation in sport, and officials came out saying enough is enough.
"The international sports authorities, especially the IOC, must hit very very hard. It can't continue like this," French athletics chief Bernard Amsalem Told France Info radio.
"I recommend that you must deny the Russians participating at the Olympics in Rio, regardless of the sport."
German Olympic Sports Confederation chairman Michael Vesper spoke of "a hit below the below the belt for the entire Olympic Movement."
The latest allegations came after the CBS network on Sunday cited a Russian whistleblower, Vitaly Stepanov, that Rodchenkov told him that four Russian Olympic champions from Sochi were doped.
Stepanov is a former official of the Russian anti-doping agency RUSADA and together with his wife, middle-distance runner Yuliya Stepanova, made allegations of systematic doping in Russian sports in a documentary of German network ARD broadcast in December 2014 which led to the suspension of Russian athletics and RUSADA.
Aware of the planned New York Times report, Russian sports minister Vitaly Mutko told the TASS news agency Wednesday that "Information attacks against the Russian sports are still underway" as he alleged the reports came to "for instance, to influence the course of restoration of the Russian field and track athletics’ rights. To influence improvement of our relations with WADA."
Mutko was quoted by TASS Friday of naming the accusations "absolutely groundless" and added: "I believe in these athletes."
Two of the athletes, bobsleigh gold medal winner Alexander Zubkov and Olympic 50km cross-country skiing champion Alexander Legkov, also rejected the doping accusations.