IOC president Thomas Bach on Monday vowed "zero tolerance" for any Olympics athletics results tainted by doping, but the head of world athletics said new revelations were part of a campaign to "redistribute" medals.
Allegations of mass doping made by German broadcaster ARD and the Sunday Times newspaper of Britain have plunged athletics into a new cheating crisis less than three weeks before the world championships start in Beijing.
ARD and the Sunday Times obtained an athletics world body database that they said indicated up to one third of medals involving endurance events at world championships and Olympics from 2001 to 2012 were won by competitors who have given suspicious doping tests.
"If there should be cases involving results at Olympic Games, the IOC will act with zero tolerance with our usual policy," Bach told a press conference in Kuala Lumpur.
"But at this time we have nothing more than allegations and we have to respect the presumption of innocence for the athletes." International Association of Athletics Federations (IAAF) president Lamine Diack told an IOC meeting that the world body would answer the allegations.
"Behind all this there is a desire to redistribute medals, take care of this," Diack, who will stand down as IAAF president this month, warned IOC members.
It is the second time in seven months that the IAAF has been thrown onto the defensive by doping. An ARD documentary in December claimed there was widespread doping in Russian athletics.
Both sets of allegations are being investigated by the World Anti-Doping Agency (WADA) which said it was "very alarmed".
Athletics chiefs around the world have called for a thorough inquiry.
"The accusations made must be properly investigated. We welcome the World Anti-Doping Agency's decision to probe the allegations made," said Athletics Australia president Phil Jones.
ARD and the Sunday Times newspaper said a "whistleblower" had handed over the IAAF database giving details of 12,000 blood tests from 5,000 competitors which revealed "extraordinary" levels of doping.
Russian and Kenyan athletes feature strongly in the new claims.
A large number of the "abnormal" results were from Russian athletes, said the reports. "A remarkable 80 per cent of Russia's medal winners had recorded suspicious scores at some point in their careers," the Sunday Times said.
But Russia's Sports Minister Vitaly Mutko called the new allegations "nonsense" that were part of a power struggle within IAAF before its election for a new president this month.
Former British runner Sebastian Coe and pole vault legend Sergey Bubka are standing for the IAAF presidency. Both have called for a tough response to doping in athletics.
ARD said there was "massive corruption" within Kenya's athletics establishment and "a desire to cover-up doping... to the summit of the Kenyan athletics federation".
The ARD/Sunday Times reports also said: - More than 800 athletes among those on the database recorded blood tests which experts said were "highly suggestive of doping or at the very least abnormal".
- The tests showed an increasing use of blood transfusions and hard-to-detect EPO micro-doses to boost red cell count and performances.
- In some finals at the Olympics and world championships, every athlete in the three medal positions had recorded a suspicious blood test.
Robin Parisotto, one of two Australian experts who studied the results, said: "Never have I seen such an alarmingly abnormal set of blood values. So many athletes appear to have doped with impunity, and it is damning that the IAAF appears to have idly sat by and let this happen." Adam Pengilly, a British member of the IOC, said Monday that the IAAF has been "quiet" over the past year and should do more to "promote clean athletics".
The IAAF has promised to release a statement quickly on claims that it has failed to act on evidence.
Any sanctions are likely to be a drawn-out process however, as the WADA investigation will be extended by the new allegations.
WADA president Craig Reedie has called the new allegations "very disturbing" and said they would "once again, shake the foundation of clean athletes worldwide".
Reedie had hoped to receive a report from an independent commission in September on the earlier allegations on doping in Russian athletics. This will now be pushed back by the new claims, he said.