Twenty-three athletes who competed in the London 2012 Olympic Games returned adverse analytical findings on doping tests after samples were reanalysed, the International Olympic Committee has announced.
The results, which were taken from 265 selected doping samples, cover five different sports and six different nationalities and were all based on intelligence-gathering that began in August 2015.
The IOC say the reanalysis programme is ongoing, with the possibility of more results in the weeks to come.
Last week the IOC announced that up to 31 athletes could be banned from competing at Rio 2016 after the reanalysis of 454 samples from the 2008 Olympic Games in Beijing.
In the meantime, one more sample from Beijing 2008 has shown abnormal parameters, which the IOC and the respective international federation will follow up.
"These reanalyses show, once again, our determination in the fight against doping," said IOC president Thomas Bach.
"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 IOC say the reanalysis of samples from Beijing and London was performed using the latest scientific methods.
The reanalysis follows work with the World Anti-Doping Agency (WADA) and the international federations over the last 10 months.
It was mainly focused on athletes who could potentially participate in Rio.
The athletes, National Olympic Committees and international federations concerned are already being informed, after which the proceedings against the athletes can begin.
All athletes found to have infringed the anti-doping rules will be banned from competing at Rio.