World athletics' governing body has suppressed a 2011 survey that reveals that up to a third of the world's top competitors admitted using banned performance-enhancing techniques, Britain's Sunday Times and German broadcaster ARD/WDR reported.
The authors of the study, which involved interviews with 1,800 athletes at the 2011 world championships in South Korea, were told to sign a confidentiality agreement a month after the information had been collected and analysed, the newspaper said.
The revelations are the latest in a series of damaging blows for the sport in the countdown to the start of this year's world championships in Beijing on August 22.
Earlier investigations by ARD and the Sunday Times prompted claims that more than 800 athletes tested between 2001 and 2012 had suspicious test results that were not followed up by the IAAF.
The IAAF has since initiated disciplinary action against 28 athletes after retesting samples from the 2005 and 2007 world championships with new technology that can uncover previously undetectable substances.
The organisation came under heavy fire from the authors of the 2011 study, which was conducted by researchers at the University of Tuebingen in Germany and leaked to The Sunday Times and ARD/WDR.
"The IAAF's delaying publication for so long without good reason is a serious encroachment on the freedom of publication," a statement from the researchers said.
The statement added that the IAAF had not commissioned the survey but had used its influence to suppress the findings.
The IAAF told the newspaper that it was still in negotiations with the study authors and the World Anti-Doping Agency (WADA) about its publication.
The results of the study showed that 29-34 percent of the 1,800 competitors at the championships had violated anti-doping rules in the previous 12 months.
"These findings demonstrate that doping is remarkably widespread among elite athletes and remains largely unchecked despite current biological testing programmes," the study said.
The study was financed by WADA, which told the newspaper on Friday that they had given the IAAF the power to veto publication in return for allowing access to the athletes at the 2011 championships.
The lead author, Rolf Ulrich, said he and his fellow experts had been barred from even discussing their work.
"The IAAF is blocking it," Ulrich told the newspaper. "I think they are stakeholders with WADA and they just blocked the whole thing."
Some of the study's headline figures were leaked in America in 2013, but the IAAF continued to prevent full publication, the newspaper said.