"The International Olympic Committee (IOC) announced today that reanalysis of the "A" samples from 23 athletes in five sports and from six National Olympic Committees (NOCs) who competed at the Olympic Games London 2012 has returned Adverse Analytical Findings (AAFs)," the IOC said in a statement.
Previously, the IOC retested hundreds of samples from the 2008 Beijing games. Over 30 athletes from six sports could be banned from taking part in the upcoming Summer Olympics due to take place in Brazil's Rio de Janeiro in August.
Reanalysis of London 2012 Olympic champions continues, the IOC said, adding that more results may be released in the coming weeks.
"The athletes, NOCs and IFs [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 the Olympic Games Rio 2016," the IOC's statement said.
The IOC and the World Anti-Doping Agency (WADA) also plan to investigate allegations of doping misconduct at Russia's Sochi laboratory during the 2014 Olympics. Russian Sports Minister Vitaly Mutko dismissed all accusations as "absurd" stressing that Moscow had already embraced all recommendations made by international sports organizations and ensured proper doping control.
In November 2015, WADA's Independent Commission issued a report accusing Russia of numerous breaches of global anti-doping regulations. As a result, the IAAF temporarily suspended the Russian Athletic Federation's membership.