Tour de France [Images] winner Floyd Landis firmly denied committing a doping offence on Friday and said he would prove he has naturally high testosterone levels.

The 30-year-old American tested positive for the male sex hormone after an astounding comeback to win stage 17 in the French Alps, just a day after a disastrous showing which all but knocked the Phonak rider out of contention.

"I would like to be absolutely clear that I am not in any doping process," Landis told a news conference in Madrid in his first appearance 24 hours after news of his positive test was made known.

"As always, since I have cycled, my physiologic parameters of testosterone and epitestosterone are high, as are those of any other sportsman. In special cases, as in mine, for natural reasons, this level is higher still," he said.

Landis will ask for a second urine sample to be tested but his lawyer Luis Sanz said he fully expected the B test to be positive -- a result which would strip him of his Tour title and result in a probable two-year ban.

It would be the first time a Tour champion has been disqualified for doping and a nightmare ending for a race that was marred before it began when nine riders were forced to pull out after being implicated in a doping investigation.

Sanz said Landis would undergo hormone tests to show that his testosterone levels are naturally high and had previously hit similar levels as those tested during the Tour.

"Until the research is carried out, I ask not to be judged and much less sentenced by anybody," Landis said, his eyes welling up with tears.  

"My Tour de France win was solely and exclusively the result of many years of training, of my absolute dedication to this sport, of the sacrifice of my whole life to reach my dream."

Landis started cycling at the age of 15 and was taken under the wing of seven-times Tour winner Lance Armstrong [Images] before switching to the Phonak team in 2005.

Phonak said Landis would be dismissed if the B result, which may come out on Monday, was positive. Landis said he intended to continue racing once he has had an operation on his hip.

DOPING CRACKDOWN

Cycling has been blighted by a long history of doping and tour organisers said Landis's test and the pre-race doping case showed they were cracking down more heavily on transgressors.

"It is obvious that those who continue to cheat can expect a really tough time," said Tour director Christian Prudhomme.

However, the head of the World Anti-Doping Agency Dick Pound said the world cycling body UCI still had work to do to tighten their testing procedures and clean up the sport's image.

Officials and riders said there should be no mercy if Landis's test is confirmed positive.

"Our sport's survival is at stake," said Patrick Lefevere, the president of the Association of professional cycling teams.  

German Andreas Kloeden, who came third in the Tour, said he would feel cheated if Landis's victory was tainted.

"We all enter the race believing that each cyclist is successful through discipline and hard work and when someone is pulled out then sure, we feel betrayed," he said.

If the test is confirmed the American federation USA Cycling will have a month to decide whether to ban Landis. Meanwhile, the Tour organisers will hand victory to Spain's Oscar Pereiro, who finished second overall.

Landis's lawyers could take the matter to the Court of Arbitration for Sport (CAS), a potentially long procedure.

Landis has said that after a disastrous 16th stage, when he lost the yellow jersey after falling apart on the ascent to La Toussuire, he drowned his sorrows in whiskey and beer with his teammates.

Asked if the alcohol intake could have affected his testosterone level before his remarkable stage victory a day later, the diminutive rider shrugged, smiled nervously and said: "That would be speculation but I hope not."

"I still feel satisfied I won the race and knowing how I did it. I deserved to win the race. I was the strongest guy there."