Armstrong has furiously denied the allegation which has been leveled at him several times before.
French sporting daily L’Equipe headlined the story “Armstrong’s Lie” on its front page, and reported that his use of the illegal blood booster EPO (erythropoeitin) was revealed in tests by a French laboratory of frozen urine samples taken during the 1999 Tour.
The 33-year-old American, who retired in July after coasting to his record seventh Tour title, wasted no time in scorning the accusations.
“Yet again, a European newspaper has reported that I have tested positive for performance-enhancing drugs,” said Armstrong said in a statement on his web site, www.lancearmstrong.com.
“L’Equipe, a French sports daily, is reporting that my 1999 samples were positive,” he continued.
“Unfortunately the witchhunt continues and the article is nothing short of tabloid journalism.
“I will simply restate what I have said many times: I have never taken performance enhancing drugs.”
The Discovery Channel team leader, who is famous for beating cancer, has issued many such denials in the past.
But his domination of the race since 1999, just 18 months after he had recovered from the illness, has always aroused suspicion in France, which developed stringent anti-doping laws after the 1998 Tour was all but wrecked by doping scandals.
Traces of EPO had been found on six different occasions in Armstrong’s 1999 urine samples by the national doping testing laboratory of Chatenay-Malabry near Paris, L’Equipe said in Tuesday’s report.
EPO can boost performance by 30 percent, according to experts.
The report said urine tests for EPO were not as advanced in 1999 as they are now, with more modern testing methods becoming common after 2000 at the Sydney Olympics and the 2001 Tour de France.
The urine samples, taken in 1998 and 1999, were tested in 2004 by the Chatenay-Malabry laboratory, which itself fine-tuned the testing system, according to the report.
The newspaper said 12 samples had revealed EPO use, including six from Armstrong.
It did not identify to which cyclists the other six positive urine samples belonged.
“Of course it cannot be regarded as a positive test in the strict regulatory sense,” the newspaper said, claiming that there was no question of sanctions as a result of the findings.
But it said the findings could have consequences, with the World Anti-doping Agency studying possible legal channels.
Armstrong tested positive for drugs only once, during the 1999 Tour de France.
However he was cleared when his team, US Postal, produced a medical certificate showing that he used a cream to ease a pain on his saddle containing a banned corticosteroid.
French suspicions were further fuelled in 2001 when it emerged he had been working with notorious Italian sports doctor Michele Ferrari, suspected in Italy of distributing and administering banned products to a number of top athletes.
Armstrong admitted his “periodic collaboration” with Ferrari, who last year was handed a one-year suspended sentence for sports fraud.