Britain's Sunday Times newspaper and German broadcaster ARD/WRD say they have been given access to the results of 12,359 blood tests given by more than 5,000 athletes over 11 years.
When analysed by scientists, the tests showed more than 800 athletes had given blood samples that were "highly suggestive" of doping or "abnormal", reported the BBC, who added they had also seen the documents.
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The Sunday Times has reported, with the headline 'Revealed: Sport's dirtiest secret', that the data seen from the leak shows an "extraordinary extent of cheating" in elite athletics.
The BBC report said a third of medals in endurance events at the Olympics and world championships between 2001 and 2012 were won by athletes who have recorded "suspicious tests".
The investigation used two of the world's "foremost anti-doping experts", scientists Robin Parisotto and Michael Ashenden, to review the data.
An independent commission is already investigating previous allegations of mass doping.
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  • A third of medals (146, including 55 golds) in endurance events at the Olympics and World Championships between 2001 and 2012 were won by athletes who have recorded suspicious tests. It is claimed none of these athletes have been stripped of their medals.
  • More than 800 athletes - one in seven of those named in the files - have recorded blood tests described by one of the experts as "highly suggestive of doping or at the very least abnormal".
  • A top UK athlete is among seven Britons with suspicious blood scores.
  • British athletes - including Olympic champion heptathlete Jessica Ennis-Hill - have lost out in major events to competitors who were under suspicion.
  • 10 medals at the London 2012 Olympics were won by athletes who have dubious test results.
  • In some finals, every athlete in the three medal positions had recorded a suspicious blood test.
  • Athletes are increasingly using blood transfusions and EPO micro-doses to boost the red cell count.
Although abnormal blood tests are not in themselves proof of doping, the release of the data will be a huge embarrassment to the International Association of Athletics Federations less than a month before its World Championships in Beijing.
The IAAF introduced biological passports for athletics as part of its drug testing regime in 2009, which help in the detection of abnormal fluctuations in red blood cell counts.
Athletes, most notoriously in cycling, have used blood transfusions and the stimulating agent Erythropoietin to increase their red blood cell count, which can help improve performance in endurance events.
"We have to wait for the transcript of this before commenting," IAAF General Secretary Essar Gabriel told reporters on Sunday.
IAAF President Lamine Diack, who is stepping down later this month, said he was not aware of the programme.
"If you have seen it you can tell me what it says," he said, speaking at the International Olympic Committee session in Kuala Lumpur.
The World Anti-Doping Agency on Sunday said it was alarmed by the size and extent of "wild" doping allegations.
"These are wild allegations, wide allegations and we will check them out and have that done with the commission as quickly as possible," WADA chief Craig Reedie told reporters in Kuala Lumpur.
"I am very surprised by the numbers from the leak from the IAAF I am sure they will want to look at it closely to determine the source," Reedie said.
"It was the spread of the allegations that came from previous programmes (that surprised me). If you look at allegations on blood issues... they are even wider. So that's a concern. But I stress athletes are innocent until proven guilty."
'Revealed: Sport's Dirtiest Secret' - The Sunday Times
"The data shows that athletics is in the same “diabolical state” as cycling in the scandal-hit era of Lance Armstrong, according to world experts who describe the findings as a “shameful betrayal” of clean athletes. Russia emerges from the files as the blood-doping centre of the world, with more than 80% of the country’s medals won by athletes who had given a suspicious blood test at some point in their career. Kenya, renowned for producing great distance-runners, is also a doping hotbed, with questions over 18 of the country’s medals."
'Shocking exposure shows extent to which cheating is rife' - The Sunday Telegraph
"Athletics has been rocked by another drugs scandal following claims that one in three medallists in distance events at the sport’s most prestigious competitions returned suspicious tests. Criticising the IAAF for catching and punishing only a tiny fraction of these athletes despite being aware of the scale of the problem, leading expert in blood doping Michael ­Ashenden accused it of "a shameful ­betrayal of their primary duty to police their sport”."
'Athletics hit by fresh doping crisis from shock report' - The Mail on Sunday
"Athletics was in fresh crisis on Saturday night after extraordinary claims from a German TV documentary which alleged that analysis of elite athletes’ blood values showed that at least one in three medal winners at track endurance events between 2001 and 2012 had been doping. Russia will be under more pressure to be kicked out of world athletics after the claims, with The Mail on Sunday understanding that senior figures in the anti-doping world were already prepared to call for nations such as them to be banned from athletics, as evidence stacks up of widespread doping abuse."
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Cheating by the use of banned substances has long been a scourge of athletics, from the systematic doping in the former East Germany, through Ben Johnson's disqualification from the 1988 Olympics to the BALCO scandal in the United States.
Sebastian Coe, who is expected to be elected the new president of the IAAF later this month, has said he will set up a new anti-doping body specifically for athletics.
The British athletics legend is running against fellow former Olympic champion Sergey Bubka in the election, which will take place on August 19 in Beijing.
"The gap between the positive test and sanction must be reduced,” Coe said earlier this year. It would cost more money, but I’d find it. I’d have to. It would remove the conspiracy theories.”
The landscape of the sport ahead of that election has clearly now changed enormously.
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