The International Olympic Committee announced today that 23 athletes who competed at the 2012 Games in London failed a retrospective doping test. The news comes one week after the IOC announced that it would begin proceedings against 31 athletes who violated anti-doping rules during previous olympic games.

The 23 athletes come from five different sports and six countries, but the IOC hasn't yet revealed their identities. If they're found to have infringed the anti-doping rules, the IOC will ban them from competing in this summer's Olympic Games in Brazil.

The samples, all of which were taken during the London Games, were retested "using the very latest scientific analysis methods," according to a statement by the IOC. This implies that previous technologies weren't as accurate. But better technology probably isn't the reason why the IOC initiated retests. The launch of the IOC's retesting campaign this month coincided with the news that a former head of Russia's official anti-doping laboratory had swapped and destroyed athletes' samples.

The IOC has retested 454 doping samples from the 2008 Beijing Games, as well as 265 samples from the 2012 Games. It will continue retesting samples, so it's possible that other results like these will surface in the coming weeks. "We want to keep the dopers away from the Olympic Games in Rio de Janeiro," IOC president Thomas Bach said in the statement. "This is why we are acting swiftly now."