The use of the gas xenon to improve the performance of athletes is not banned and there would be "nothing wrong" if Russian athletes were using it, a top Russian medical official said Wednesday.
Germany's WDR television this week and other reports this month claimed that top Russian athletes have been using xenon to improve their performance at Olympic Games from Athens 2004 right up to the just completed Sochi 2014 Winter Games.
Inhaling the gas encourages the production in the body of the hormone Erythropoietin (EPO) which encourages the formation of red blood cells in the body to improve performance.
Externally injecting EPO is regarded as flagrant doping and its illegal use became notorious in particular among cyclists in the Tour de France.
The use of another method to stimulate the natural production of EPO inside the body is not outlawed and regarded by many experts as a grey area.
The head of Russia's Federal Biomedical Agency (FMBA), in the first reaction by a Russian official to the reports, said it was possible the gas was being used by Russian athletes, without confirming further.
"Xenon is not an illegal gas," said FMBA chief Vladimir Uiba, quoted by Russian news agencies. "We have a principle not to use what is forbidden by the World Anti-Doping Agency (WADA)."
"It is possible that our sportsmen have been using xenon inhalators but there is nothing wrong with that.
"We use what is not illegal, is not destructive and does not have side effects," he added.
Russia's athletes enjoyed a hugely successful Winter Games in Sochi, winning 13 gold medals and topping the final medals table.
The country until recent years had a dire reputation for the doping of athletes dating back to the Soviet system. However Russia has now take steps to clean up its act including the creation of its own anti-doping agency RUSADA.
According to a report in The Economist in early February, a document formulated by the research institute of the Russian defence ministry in 2010 set out guidelines for the administration of xenon gas to athletes.