Seven-time Tour de France winner Lance Armstrong again faces allegations that he used performance-enhancing drugs, after a French newspaper reported that urine samples taken in 1999 tested positive for a red blood cell booster.

In a four-page article headlined "The Armstrong Lie," the sports daily L'Equipe printed copies of documents suggesting six urine samples he provided during his first championship contained erythropoietin, or EPO. The drug was on the list of banned substances at the time but there was no effective test to detect it.

Tour de France director Jean-Marie Leblanc said the report published Tuesday appeared credible and meticulously researched, adding that Armstrong must have a chance to rebut the claims.

"We are very shocked, very troubled by the revelations we read this morning," Leblanc told RTL radio.

Armstrong, a frequent target of L'Equipe, vehemently denied the allegations.

"Unfortunately, the witch hunt continues and tomorrow's article is nothing short of tabloid journalism," he wrote on his Web site. "I will simply restate what I have said many times: I have never taken performance-enhancing drugs."

The allegations surfaced seven years later because EPO tests on the 1999 samples were carried out only last year -- when scientists at a lab outside Paris used them for research to perfect EPO testing. The national anti-doping laboratory in Chatenay-Malabry said it promised to hand its finding to the World Anti-Doping Agency, provided they were never used to penalize riders.

L'Equipe's investigation was based on urine B samples -- the second of two samples used in doping tests. The A batch was used in 1999 for analysis at the time. Without those samples, any disciplinary action against Armstrong would be impossible, French Sports Minister Jean-Francois Lamour said.

The governing body of world cycling did not begin using a urine test for EPO until 2001, though it was banned in 1990. For years, it had been impossible to detect the drug, which builds endurance by boosting the production of oxygen-rich red blood cells.

Jacques de Ceaurriz, the head of France's anti-doping laboratory, which developed the EPO urine test, told Europe-1 radio that at least 15 urine samples from the 1999 Tour had tested positive for EPO.

Separately, the lab said it could not confirm that the positive results were Armstrong's. It noted that the samples were anonymous, bearing only a six-digit number to identify the rider, and could not be matched with the name of any one cyclist.

However, L'Equipe said it was able to make the match.

On one side of the page, it showed what it claimed were the results of EPO tests from anonymous riders used for lab research. On the other, it showed Armstrong's medical certificates, signed by doctors and riders after doping tests -- and bearing the same identifying number printed on the results.

"It will be very interesting to see what UCI does and what the U.S. Cycling Federation does and what Lance Armstrong has to say," WADA chairman Dick Pound said. "If the evidence is seen as credible then, yes, he has an obligation to come forward and specifically give his comments, especially after his previous comments that he has never used drugs. If anything were found, we couldn't do anything because we didn't even exist in 1999. But it's important that the truth must always be made clear."

Representatives for Armstrong said he was in Austin, where he lives and did not wish to comment beyond the statement on his Web site.

Armstrong has been dogged by questions in the French media about how someone whose testicular cancer had spread to his lungs and brain could rise to the top of one of the most grueling sporting events in the world.

Armstrong and his U.S. Postal Service team became the subject of a French investigation into whether they used banned substances during the 2000 race. The probe was closed in 2002 for lack of evidence.

L'Equipe, whose parent company is closely linked to the Tour, often questioned Armstrong's clean record and frequently took jabs at him -- portraying him as too arrogant, too corporate and too good to be for real.

"Never to such an extent, probably, has the departure of a champion been welcomed with such widespread relief," the paper said the day after Armstrong's record seventh straight win.

A former L'Equipe journalist, Pierre Ballester, was co-author of a book published last year that contained doping allegations against Armstrong. He wrote "L.A. Confidential, the Secrets of Lance Armstrong" with the Sunday Times sportswriter David Walsh.

In the book, one of Armstrong's former assistants claimed that the American once asked her to dispose of used syringes and give him makeup to conceal needle marks on his arms.

Armstrong has taken libel action against the Sunday Times after the British newspaper reprinted allegations in a review of the book in June 2004. The case is to go to trial in London's High Court in November.

Victor Hugo Pena, Armstrong's former U.S. Postal Service teammate, said the French were bad losers who could never accept his supremacy on the Tour.

"What Lance achieved nobody can take away," Pena, who helped Armstrong to three of his seven Tour victories, told Colombia's Caracol radio Tuesday. Pena said Armstrong was so closely watched during the Tour that it would've been hard for him to use performance-enhancing drugs.

"Not only did the sports laboratories constantly test him, but video cameras were set up in his room and police agents constantly monitored Lance's movements and who was visiting him and even his phone conversations," Pena said.

Armstrong retired from cycling after his record seventh Tour victory last month. In his parting speech, he addressed the people who believe he was doping.

"I'm sorry for you," Armstrong said. "I'm sorry you don't believe in miracles."

The French sports daily l'Equipe says Lance Armstrong used the performance-enhancing drug EPO to win the Tour de France in 1999.