Lausanne - In a major doping crackdown stretching back eight years, 31 athletes in six sports were caught in retesting of samples from the 2008 Beijing Olympics and other positive cases could emerge from the 2012 London Games, the IOC said Tuesday.
The International Olympic Committee opened disciplinary proceedings against the 31 unidentified athletes from 12 countries who competed in Beijing and were planning to take part in the Rio de Janeiro Games in August.
The positive cases emerged from the recent retesting of 454 doping samples from Beijing with "the very latest scientific analysis methods," the IOC said. The Olympic body stores samples for 10 years to allow for retesting with improved techniques.
The IOC said it would inform the relevant national Olympic committees in the coming days.
"All those athletes infringing anti-doping rules will be banned from competing at the Olympic Games" in Rio, the IOC said after a teleconference meeting of its policy-making executive board.
Results of retesting of 250 samples from the London Olympics will be announced shortly, the IOC said. Those tests were also aimed at athletes planning to compete in Rio.
The IOC said it would also undertake a "wider retesting program" of medallists from both the Beijing and London Games. Samples of athletes who could be promoted to medals following disqualification of drug cheats will also be retested.
The IOC also asked the World Anti-Doping Agency to launch a "fully-fledged investigation" into allegations that the drug-testing system at the 2014 Winter Games in Sochi was subverted by Russian officials.
The IOC said it would ask the Lausanne anti-doping lab and WADA to proceed with analysing Sochi samples "in the most sophisticated and efficient way possible."
Grigory Rodchenkov, the former head of the Russian anti-doping laboratory, told the New York Times last week that he switched tainted urine samples for clean ones for Russian athletes who were part of a state-sponsored doping program. He has offered to assist in retesting.
The statute of limitations for retesting was extended in 2015 from eight to 10 years, meaning the Beijing samples remain valid through 2018.
It's not the first time that samples from Beijing have been retested. A few months after those games, the IOC reanalysed nearly 1,000 of the total of 4,000 samples with a new test for the blood-boosting drug CERA. Five athletes were caught, including 1,500-meter gold medalist Rashid Ramzi of Bahrain.
Nearly 500 doping samples from the 2006 Winter Olympics in Turin have already been retested. The IOC has not disclosed whether those retests had produced any positive cases.
Five athletes were caught in retests of samples from the 2004 Athens Olympics, including men's shot put winner Yuriy Bilonog of Ukraine.
On a separate issue, the IOC said it would "work to shed full light" on bribery allegations tied to Tokyo's winning bid for the 2020 Olympics.
French prosecutors said last week that 2.8 million Singapore dollars ($2 million) was apparently transferred from Japan to the Singapore account of a company tied to the son of former IAAF President Lamine Diack, who is facing corruption charges.
Tokyo bid leaders acknowledged the payments were made, but said they were for legitimate consulting fees.
The IOC said it would remain a civil party to the French investigation and its chief ethics officer would "actively cooperate" in the inquiry.