Allegations that the Russian state organised and covered up doping at the Sochi Olympics are "a turncoat's libel", according to Russian president Vladimir Putin's spokesman.
Dmitry Peskov attacked the credibility of former Russian anti-doping official Grigory Rodchenkov, who told the New York Times that he switched tainted urine samples for clean ones during the Olympics.
Mr Rodchenkov also said he believed the Russian security services had helped to cover up doping.
Mr Peskov said he "wouldn't put trust in such unfounded claims".
Earlier, two Russian Olympic gold medallists denied doping after they were named in the New York Times article.
Bobsledder Alexander Zubkov and cross-country skier Alexander Legkov told Russian state TV that they were clean during the Olympics.
Mr Zubkov said the article is "baseless libel," while Mr Legkov defended his "honest medals" and casts doubt on the credibility of Mr Rodchenkov.
Mr Zubkov was a surprise gold medallist in the two-man and four-man bobsled in Sochi at the age of 39, and also carried the Russian flag in the opening ceremony.
Mr Legkov won gold in the 50-kilometre men's cross-country skiing.