Turning to new technology to uncover previously undetected substances, the IAAF has initiated disciplinary action against 28 athletes after retested samples from the 2005 and 2007 World Championships found 32 adverse doping findings.
World athletics' governing body said on Tuesday it could not name the 28 yet, "due to the legal process".
"A large majority of the 28 are retired, some are athletes who have already been sanctioned, and only very few remain active in sport," the body said. "The IAAF is provisionally suspending them and can confirm that none of the athletes concerned will be competing in Beijing."
If violations are confirmed the IAAF said it would correct the record books for the 2005 and 2007 world championships and re-allocate medals as necessary.
The 2005 event was staged in Helsinki, with Osaka, Japan, hosting two years later. The 2015 World Championships start in the Chinese capital on Aug. 22.
The IAAF said its retesting had begun in April, "well before the most recent allegations made against the IAAF by the ARD and The Sunday Times".
The re-testing took advantage of new testing procedures and the 10-year period now offered under IAAF rules and the World Anti-Doping Code.
"The latest scientific breakthroughs in anti-doping technology and analysis have been employed in the re-analysis of these samples to allow us to find previously undetectable substances," Martial Saugy, director of the Swiss Laboratory for Doping Analyses in Lausanne, said in a statement.
Beginning in 2005, athletes' samples from previous championships have been stored at the laboratory and they were used in the re-analysis.
"The findings reconfirm, yet again, the commitment of the IAAF to target and uncover all cheating in the sport, no matter how long it takes," said the IAAF, which was heavily criticised for its anti-doping efforts earlier this month by German broadcaster ARD and Britain's Sunday Times newspaper.
The testing was the second of samples from the 2005 Helsinki championships. The first, in 2012, revealed six adverse findings and to date nine athletes have been sanctioned after re-tests of samples from various world championships.
"The IAAF does not shy away from the fact that some athletes continue to cheat and defraud their fellow competitors," the federation said in its statement. "But we will do everything in our power, and use every tool available to protect those clean athletes who form the large majority of our sport."
