World athletics' governing body has been accused of blocking a survey that revealed a third of top athletes admitting cheating.
The International Association of Athletics Federations (IAAF) allegedly stopped the study, which was carried out in 2011, from being published and prevented its authors from speaking about it, according to the Sunday Times.
The University of Tubingen in Germany, which led the research, is quoted as saying in the paper: "The IAAF's delaying publication for so long without good reason is a serious encroachment on the freedom of publication."
Researchers compiled the information from athletes who competed at the world championships in Daegu, South Korea, four years ago. The results reportedly show that 29-34% of the 1,800 competitors had confessed to using banned performance-enhancing techniques 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," they concluded.
When asked about the study - which was financed by the World Anti-Doping Agency (WADA) - being held back, lead author Rolf Ulrich said: "The IAAF is blocking it. I think they are stakeholders with Wada and they just blocked the whole thing."
The IAAF is quoted as saying: "Discussions are ongoing with the research team and Wada regarding publication."
It comes against a backdrop of doping allegations in world athletics.