Twenty-three athletes from five sports tested positive for banned drugs in re-checks of 265 samples from the London 2012 Olympics, the International Olympic Committee said on Friday.
The IOC added that the athletes were members of six national Olympic Committees four years ago.
Last week the organisation found 31 athletes from six sports who could be banned from the Rio de Janeiro Games in August after failing doping tests when 454 samples were re-examined from the 2008 Beijing Olympics.
The IOC, which said one more sample from Beijing had shown “abnormal parametres” and would also be followed up on, added that the re-testing programme was ongoing and could deliver more positive checks in the coming weeks.
“These re-analyses show, once again, our determination in the fight against doping,” said president Thomas Bach. “We want to keep the dopers away from the Olympic Games in Rio de Janeiro.
“I have already appointed a disciplinary commission which has the full power to take all the decisions on behalf of the IOC.”
The IOC, which stores samples for a decade in order to allow for re-testing with newer methods or to look for new drugs, will not name the athletes or the sports until the second samples have been tested. That process can take several weeks.
Doping scandals have plagued the buildup to the world’s biggest multi-sports event with Olympic powerhouse Russia under investigation following a report by the World Anti-Doping Agency suggesting systematic doping in that country.
Russia has confirmed 14 of the positive Beijing Games rechecks concerned their athletes, some medallists among them, in a further blow to its credibility.
Track and field athletes from Russia are currently suspended pending an investigation into the scandal that has rocked world sport and could leave the nation without a full team at the Games that start on Aug. 5.
The IAAF, the governing body of athletics, will decide on June 17 whether Moscow has done enough to clean up its act in order to be readmitted to competition.
Russia has pledged to ban all athletes with a doping past from its Olympic squad.
Calls for a blanket ban of the entire team have grown louder with every twist of the scandal, though.
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