Canton of Vaud: The International Olympic Committee on Friday reported 23 new doping failures from retests on 265 samples from the 2012 London Games.
The 23 were from six countries and took part in five different sports. The revelation came one week after the IOC said 31 new cases had been found from 2008 Beijing Olympics.
"Reanalysis of the `A` samples from 23 athletes in five sports and from six National Olympic Committees who competed at the Olympic Games London 2012 has returned Adverse Analytical Findings," the IOC said in a statement.
The IOC began re-testing samples following revelations by the World Anti-Doping Agency (WADA) last year showing systematic cheating among Russian athletes, likely with state support.
A total of 454 samples from Beijing have been retested, the IOC said, adding that a 32nd case from the Games in the Chinese capital had shown "abnormal parameters" with further investigation pending.
The re-testing programme is focused on athletes who could compete in the upcoming Rio Games.
"These reanalyses show, once again, our determination in the fight against doping," IOC President Thomas Bach said in the statement.
"We want to keep the dopers away from the Olympic Games in Rio de Janeiro," he added. "This is why we are acting swiftly now."
The IOC has informed the athletes whose sample have failed on reanalysis, but will not name them until a final confirmation test is carried out.
"All athletes found to have infringed the anti-doping rules will be banned from competing at the Olympic Games Rio 2016," the statement said.
More failures could be coming, the Lausanne-based Olympics body said, noting that "the reanalysis programme is ongoing, with the possibility of more results in the coming weeks."