Athletics is facing a new doping crisis after a cache of leaked data from the sport's governing body revealed more than 800 athletes recorded suspicious blood tests between 2001 and 2012.
The Sunday Times newspaper and German broadcaster ARD obtained the data, which covers 12,000 tests from 5,000 athletes, from a whistleblower at the International Association of Athletics Federations (IAAF).
The evidence reveals "the extraordinary extent of cheating by athletes at the world's most prestigious events", the Times said.
A third of medals in endurance events at the Olympics and World Championships between 2001 and 2012, including 55 golds, were won by athletes who recorded dubious blood tests, but none of them had their medals stripped, the paper alleged.
The fresh allegations have rocked the sport three weeks before the start of the World Athletics Championships in Beijing.
"Never have I seen such an alarmingly abnormal set of blood values," said Robin Parisotto, an anti-doping expert who reviewed the data.
"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."
A leading British athlete is one of seven Britons to have recorded suspicious blood scores, although stars such as Mo Farah and Usain Bolt recorded no abnormal results.
Ten medals at the London 2012 Olympics were won by suspicious athletes, while in some finals, every medal-winner recorded a dubious blood test.
The World Anti-Doping Agency (Wada) said it was "very alarmed" by the allegations and pledged to open an investigation.
"Wada is very disturbed by these new allegations that have been raised by ARD; which will, once again, shake the foundation of clean athletes worldwide," said Sir Craig Reedie, president of Wada.
"Given the nature of these allegations... they will immediately be handed over to Wada's independent commission for further investigation.
"These allegations require swift and close scrutiny to determine whether there have in fact been breaches under the World Anti-Doping Code and, if so, what actions are required to be taken by Wada and/or other bodies."