The International Olympic Committee confirms that 23 athletes from the 2012 Summer Olympic in London tested positive for banned substances following reanalysis of drug-testing samples.
The news comes after the IOC announced last week that 31 athletes could be banned from competing at the Rio Olympics in August after retests of samples taken from the 2008 Games in Beijing.
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Further analysis of 265 selected samples from the London Games returned 23 so-called adverse analytical findings from athletes in five sports from six nations, with more results to come.
"These reanalyses show, once again, our determination in the fight against doping," IOC president Thomas Bach said. "We want to keep the dopers away from the Olympic Games in Rio de Janeiro.
"This is why we are acting swiftly now. I have already appointed a disciplinary commission, which has the full power to take all the decisions on behalf of the IOC."
The Russian Olympic Committee on Tuesday confirmed that 14 athletes who represented the country at the Beijing Games failed drugs tests when re-examinations were carried out.
The IOC last week announced plans to investigate claims from the head of Russia's anti-doping laboratory at the 2014 Winter Olympics in Sochi that certain athletes from the country were part of a state-sponsored doping program to maximize home success.