(CNN) The head of the International Olympic Committee (IOC) has promised the organization will pursue a policy of "zero tolerance" if allegations of widespread doping by track and field athletes at the Olympics are proven.

Allegations published in the Sunday Times and aired in a documentary by German broadcaster ARD, claim that a third of medals awarded in the Olympic Games and world championships between 2001 and 2012 were won by athletes who recorded suspicious doping tests.

The news organizations have based their reports on a leaked database, held by the International Association of Athletic Federations (IAAF), which holds the results of 12,000 blood tests on 5,000 athletes.

"At this time we've nothing more than allegations, and we have to respect the presumption of innocence," IOC president Thomas Bach told reporters. "If there should be cases involving results at Olympic Games, the IOC will act with zero tolerance with our usual policy."

The tests were scrutinized by Australian doping experts Michael Ashenden and Robin Parisotto, who concluded that 800 athletes, in a range of disciplines, mostly covering endurance events from the 800 meters to the marathon, had produced "suspicious" results.

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