World Anti-Doping Agency (WADA) chief Dick Pound has said that if U.S. sprinter Marion Jones has taken banned substances she should be stripped of all her medals regardless of when she won them.

Days after the head of a controversial U.S. laboratory claimed Jones regularly used drugs to enhance her performance, Pound said it was up to the U.S. anti-doping agency to make the next move.

"If she is guilty then she should be stripped of all her medals and banned for two years," Pound told reporters on Monday at an international conference in Athens.

Asked if there was a time limit of what medals could be taken from Jones, Pound said: "That is not an issue at all."

Under International Olympic Committee (IOC) rules, athletes can only be stripped of their medals if they are caught within three years of the event.

American sprinter Jones, who won three gold medals at the Sydney Olympics in 2000, has consistently denied using drugs.

Conte, however, who is facing criminal charges on supplying illegal drugs to athletes through his Balco lab in San Francisco, told the ABC news magazine 20/20 last week he watched her using steroids having introduced her to a doping programme before the 2000 Olympics.

"There are two people saying exactly the opposite. It's up to the U.S. anti-doping agency to find out the truth," Pound said. "In this case the Balco (issue) has been to the United States what Ben Johson was to Canada. The United States is not in a position to say 'we do not have a doping problem'."

In the biggest Olympic doping scandal Canadian Johson lost his 1988 100m gold medal after testing positive for performance-enhancing drugs.

Jones, who failed to win a medal in Athens having not qualified for the individual sprint events, is already being investigated by USADA.

"If she indeed has taken drugs it is going to be a big disappointment for a lot of people. If you are big star you have more responsibility," Pound said.

USADA investigations have led to the suspension of a number of athletes including women's world sprint champion Kelli White and twice Olympic relay gold medallist Alvin Harrison.

Jones's partner, Tim Montgomery, the 100m world record holder, is appealing against a possible life ban for doping violations. His hearing will be heard in San Francisco in June.