The World Anti-Doping Agency (WADA) admitted on Wednesday (March 23) that reports in The Times Sergei Portugalov, the doctor allegedly behind the doping programme in athletics, has been encouraging swimmers in Russia to take banned substances, were "concerning".

The Times also claimed that two swimmers returned positive tests for erythropoietin, the blood-booster at the centre of the doping storm in cycling, but their results were covered up by the Russian Anti-Doping Agency.

WADA revealed they were planning to write to the International Swimming Federation (FINA) to ask them about the allegations.

FINA, however, had already claimed they were "not aware of any concrete evidence of systemic doping in Russian swimming" and that they had "taken a particularly robust approach to our anti-doping procedures in relation to Russia and Russian competitions".

In 2014 the world governing body had awarded Russian President Vladimir Putin its top honour, the FINA Order.

"All statements must be made on behalf of the International Swimming Federation," Mutko said in an interview with the Russian news agency TASS.

"The Times is not a regulating sports body and only states its own opinion.

"Today, we may encounter the case of false accusations in regard to [Russian] swimming."

More than 20 Russian swimmers have failed drugs tests since 2009, with four-time world champion Yuliya Efimova the most high-profile recent case after she tested positive for meldonium, a product only added to the WADA banned list on January 1.

Efimova won the 100 metres breaststroke title at last year's home World Championships in Kazan and is considered Russia's leading swimmer.

The 23-year-old claims to have taken meldonium for medical reasons and still hopes to compete at Rio 2016.

She has already served a 16-month ban for doping having failed for banned steroid DHEA in 2013 and is facing a lengthy suspension.