The International Olympic Committee opened disciplinary proceedings yesterday 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.
"This is a powerful strike against the cheats," IOC President Thomas Bach said. "They show once again that dopers have no place to hide."
The positive cases from Beijing emerged from the recent retesting of 454 doping samples 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, with athletes caught facing retroactive disqualification and loss of any medals.
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The IOC said it could not immediately identify the athletes caught in the Beijing retests for legal reasons, saying it would inform the relevant national Olympic committees in the coming days.
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 medalists 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 in Sochi was subverted by Russian officials.
for reliable retesting. Grigory Rodchenkov, the former head of the Russian anti-doping laboratory, told the New York Times last week that he gave Russian athletes a cocktail of drugs before the Olympics and switched tainted urine samples for clean ones during the games. 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 reanalyzed 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.
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 (USD 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.