ZURICH (REUTERS) - Russia's Mariya Savinova has been stripped of her 2012 Olympics 800m gold medal after the Court of Arbitration for Sport (CAS) on Friday imposed a four-year ban saying there was "clear evidence" she used performance-enhancing drugs.

She is the latest in a growing list of Russian athletes to have past Olympic medals taken away over doping, as the nation struggles to overcome its most widespread doping scandal ever.

The retroactive four-year penalty starts from Aug 24, 2015, but CAS also disqualified all of Savinova's results from July 26, 2010, to Aug 19, 2013, thereby stripping her of her 2011 World Championships gold, 2013 World Championships silver and 2010 European Championships gold.

South Africa's double silver medallist Caster Semenya is now in line to be promoted to gold in both the 2012 Olympics and 2011 World Championships.

The 31-year-old was among the athletes that a commission set up by the World Anti-Doping Agency (WADA) recommended be banned for life in 2015.

"On the basis of clear evidence, including the evidence derived from her biological passport, Mariya Savinova-Farnosova is found to have been engaged in using doping from 26 July 2010 through to 19 August 2013," CAS said.

It took the action as the decision-making authority while the Russian Athletics Federation (RusAF) remains banned over the country's state-backed doping scandal.

More than 100 athletes have so far tested positive in retests of samples taken during the 2008 and 2012 Olympics conducted by the International Olympic Committee (IOC).

Russia has the most positive retests per nation.