Last updated on .From the section Winter Olympics

The World Anti-Doping Agency (Wada) has promised to take action over claims Russian athletes inhaled performance-enhancing gas at the Winter Olympics.

German broadcaster WDR reports athletes used the noble gas xenon, which academic studies say causes an increase of the hormone erythropoietin (EPO).

It is forbidden to artificially increase the amount of EPO in the body.

Wada president Craig Reedie said: "Our commission which monitors the banned substance list will take on the issue."

WDR alleges that xenon has been used by the Russia for years and that the country's ministries of sport and defence recommended its use "with the aim of improving the performance of the athletes" and because the gas "is not monitored by Wada".

Using pharmaceutical methods to increase oxygen intake, thus improving performance, is banned by Wada.

But using another method to stimulate the natural production of EPO is not outlawed and regarded as a grey area by some.

Hosts Russia enjoyed a successful Winter Olympics in Sochi, winning 13 gold medals to top the medal table.