Russian doping: IOC begins proceedings against 28 Sochi 2014 competitors
Twenty eight Russian competitors face disciplinary proceedings after their urine samples from the 2014 Winter Olympics were allegedly manipulated.
The samples were highlighted in the McLaren report, which outlined a state-sponsored doping programme in Russia between 2011 and 2015.
Now the International Olympic Committee (IOC) is reanalysing the samples, which it warns could lead to sanctions.
The Russian city of Sochi hosted the 2014 Winter Olympics.
According to McLaren's report - which was commissioned by the World Anti-Doping Agency (Wada) - salt and coffee were used to manipulate Russian samples and there were also cases of female ice hockey players having male urine samples.
"This is the immediate follow-up to Professor McLaren's report," said IOC president Thomas Bach.
"The IOC will go beyond the findings of the report by reanalysing all the samples of all the Russian athletes who participated in the Olympic Winter Games Sochi 2014, as well as all those who participated in the Olympic Games London 2012."
Samples from the 2010 Winter Games in Vancouver will also be retested in the wake of the McLaren report, which stated over 1,000 Russian athletes - including medallists - had benefited from the doping programme.
Putin's anger at whistleblower
Russian President Vladimir Putin has criticised Grigory Rodchenkov, one of the whistleblowers whose information led to the report.
Rodchenkov used to head Russia's anti-doping laboratory and has admitted to doping athletes.
Putin said: "Do you know where he worked before that? In Canada. And then what did he do? He came to Russia and... kept bringing in all sorts of filth."
The 64-year-old admitted Russia "does have problems with doping" but called on Wada to be "more transparent", insisting his country "never created the problem of doping".
Russia won 72 medals at the London Games, 21 of which were gold, and 33 medals at Sochi, 13 of which were gold.
On Thursday, it lost hosting rights to a World Cup biathlon meeting set to be held in March and was stripped of a speed skating meet for the same month.
McLaren's report, published on 9 December, was a follow-up to an interim report he wrote in June, which led to some Russian athletes not being allowed to compete at the 2016 Olympics and a complete ban on the country from the subsequent Paralympics.