The 2016 Rio Olympics is now just 70 days away but the participation of 23 athletes could be under threat after doping samples taken at the London 2012 Olympics tested positive for banned substances.

In a statement, the International Olympics Committee revealed the athletes came from five sports and six different countries.

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The IOC announced that 23 athletes at the London 2012 Olympics have failed retrospective doping tests. The athletes are from five different sports and six different countries.

The tests focused on athletes who could take part in 2016 Rio Games.

“One thing is clear the IOC will act with zero tolerance to protect the clean athletes. Whoever is involved and is in the reach of the IOC will be sanctioned because this we owe to all clean athletes around the globe,” Thomas Bach, IOC president said.

The retests have been conducted using the latest scientific methods. The IOC say the program is ongoing with the possibility of more results in the coming weeks, while the World Anti-Doping Agency began the retesting process last year.

The International Association of Athletics Federations will make a decision on whether Russia’s track and field athletes will be allowed to compete at the Rio Games next month. Last year, Russia was suspended by the IAAF after being accused of state sponsored doping in a report commissioned by WADA.