Jones had always maintained her innocence

The American sprinter's initial sample had tested positive for the banned blood-boosting drug erythropoietin (EPO) in June.

"I am absolutely ecstatic," said the 30-year-old Jones, who had been facing a two-year ban from the sport had her 'B' sample tested positive.

"I am anxious to get back on the track," she added in a statement.

Interview: Marion Jones' attorney Howard Jacobs

"I have always maintained that I have never ever taken performance-enhancing drugs, and I am pleased that a scientific process has now demonstrated that fact."

Jones now hopes to compete for Team USA in next week's World Cup meet in Greece as well as in the Grand Prix event in Shanghai meeting later this month.

Her manager Charles Wells said: "This weekend's meet (the World Athletics final in Stuttgart) was too short a time to get ready, but she is hoping to compete in the World Cup and in Shanghai."

Jones's coach Steve Riddick said she would resume training on Friday.

He said: "We will get her ready as we can."

Marion was wrongfully accused of a doping violation and her reputation was unfairly questioned Howard Jacobs, Marion Jones's lawyer

Jones, who won five medals at the Sydney Olympics in 2000, had never previously failed a doping test.

She was under scrutiny by the USADA in connection with the Balco laboratory doping scandal but was never charged with any offence.

Jones has suffered a slump in form since giving birth to her first child with ex-partner Tim Montgomery in June 2003.

But in June she won the US 100m championship in 11.10 seconds.

She has three of the five fastest times in the world this year with a best of 10.91 secs to rank second overall behind Jamaica's Sherone Simpson.

Her lawyer Howard Jacobs also expressed his delight at the result.

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"The scientific part of the testing protocols worked," he said. "The 'B' sample did not confirm the 'A' positive result and Marion is now free to compete.

"But it is unfortunate that because of the 'leak' of the 'A' sample results, Marion was wrongfully accused of a doping violation and her reputation was unfairly questioned."

It is not the first time an athlete's 'B' sample has returned negative.

Olympic silver medallist Bernard Lagat was suspended for two months after testing positive for EPO in August 2003.

However, the 'B' sample cleared the Kenyan-born 1500m runner.