Triple Olympic sprint champion Marion Jones has failed an initial doping test, a source familiar with the test told Reuters.

The positive test of Jones's A sample occurred at the June US Championships in Indianapolis, the source, who did not wish to be identified, said.

US media reported the blood-boosting drug erythropoietin (EPO) had been found in Jones's urine sample.

Under anti-doping protocols, an athlete is not considered to have committed a doping offence until his or her B sample has tested positive and the athlete has been afforded an arbitration hearing.

Jones would face a minimum of a two-year ban if it is determined she has committed a doping offence.

A spokesman for the IAAF said it was unable to comment on individual cases until the result of the B sample was known or if the athlete in question had been suspended from competition.

Jones's general counsel also would not discuss the matter.

"It is unfortunate that the integrity and the confidentiality of the testing process may have been breached, but Marion Jones has always been clear, she has never taken performance-enhancing substances, not now, not ever," Rich Nichols said in a statement to Reuters.

The 30-year-old Jones has been under investigation in connection with the BALCO laboratory doping scandal although she had never failed a doping test. She withdrew suddenly from the Golden League meeting in Zurich on Friday and flew back to the United States for personal reasons, organisers said.

Jones is the third high-profile American to fail a doping test this year.

Sprinter Justin Gatlin tested positive for testosterone in April and cyclist Floyd Landis failed a test for testosterone at the Tour de France.