The ruling body of athletics said on Wednesday it had been informed in 1988 there had been eight positive dope tests at the U.S. Olympic trials, for ephedrine and ephedrine-related compounds.

But the IAAF said in a statement the athletes, whose names were not revealed, had been eligible to compete at the 1988 Olympic Games. The banned substances had been present "in low concentration", it said.

"The IAAF Medical Committee felt satisfied ... on the basis of the information received that the cases had been properly concluded by the USOC as "negative cases" in accordance with rules and regulations in place at the time and no further action was taken," the IAAF said.

"For this reason, the athletes concerned who achieved the necessary qualification performances at the 1988 U.S. Olympic Trials and who went on to compete at the Olympic Games in Seoul were eligible to do so in accordance with IAAF Rules."

Documents released in the U.S. in mid-April suggested that 19 Olympic medallists failed drug tests between 1988 and 2000 but were allowed to continue competing at the top level.