FINA executive director Cornel Marculescu said an investigation into whether the 25-year-old Australian used performance-enhancing drugs has been closed.

"There is insufficient basis to further pursue the investigation," Marculescu told The Associated Press by telephone.

Thorpe, who won five Olympic and 11 world championship titles before retiring in November, denied that he had doped. He said the high levels of testosterone and epitestosterone revealed by a urine test in May 2006 were naturally occurring.

The French newspaper L'Equipe reported the test results in March, at the time of the swimming world championships in Melbourne, sparking a wider inquiry.

Australia's sports anti-doping agency had, by that time, decided not to pursue an investigation against the retired Thorpe because it believed the levels occurred naturally, saying there was no indication Thorpe used performance-enhancing substances.

It was forced to revisit that stance when FINA appealed the decision to the Court of Arbitration for Sport.