Tour de France riders on Friday dismissed claims by shamed US cyclist Lance Armstrong that it was "impossible" to win the sport's most famous race without doping, saying his claims hit at their credibility.

Cadel Evans, who won the Tour in 2011, said he had shown it was possible to triumph without cheating, amid claims the focus was being shifted away from the start of this year's historic 100th edition of the race, which begins on Saturday.

"I think the opposite. I am proof that that is not true," the Australian BMC rider told a news conference in Porto-Vecchio, on the Mediterranean island of Corsica.

"I sometimes read in the press what Armstrong says and I respect him as a human being but really I just focus on doing my own job as best I can and fortunately we are supported by a great group of people.

"We try to do our job as we see fit and within the rules of course."

Evans' teammate, the Belgian Philippe Gilbert, blamed the media for seizing on the comments just as riders prepared for the race.

Team Sky, which includes favourite Chris Froome, said they did not want to comment.

Armstrong was asked in an interview with French daily Le Monde published on Friday whether it was possible to win without taking performance-enhancing drugs when he was riding.

He responded: "That depends on the races that you wanted to win.

"The Tour de France? No. Impossible to win without doping because the Tour is an endurance event where oxygen is decisive," he was quoted as saying by the French daily.

He added: "To take one example, EPO (erythropoetin) will not help a sprinter to win a 100m but it will be decisive for a 10,000m runner. It's obvious."

Armstrong, who won the Tour a record seven times between 1999 and 2005, later said his claims only applied to the period in which he dominated the sport.

"99-05. I was clear with Stephane Mandard (the sports editor of Le Monde) on this. Today? I have no idea. I'm hopeful it's possible," he wrote on his Twitter account @lancearmstrong.

Armstrong was last year exposed as a serial drug cheat in a devastating US Anti-Doping Agency report that plunged cycling into crisis about the extent of drug-taking in the peloton.

The Texan rider, who insisted for years that he did not take performance-enhancing drugs, was stripped of his Tour titles and banned from the sport for life.

He then admitted in a television interview that he used a cocktail of drugs, including the blood booster EPO, testosterone and blood transfusions, to win the Tour.

Armstrong told Le Monde that he was not the first athlete to dope and there would always be a doping culture but cycling was being made a "scapegoat" for the practice in all sport.

"I simply took part in this system. I'm a human being," he said, admitting that he could never erase the past but would strive to make up for it for the rest of his life.

The head of world cycling's governing body, Pat McQuaid, also disagreed with Armstrong.

"It might have been true in the past because there were undetectable substances such as EPO," the International Cycling Union (UCI) president told RTL radio.

"So everyone used EPO in cycling and other endurance sports too. But today the system is more strict and I'm convinced that you can win endurance sports by being clean and win the Tour de France by being clean."

McQuaid, who has faced calls to quit because of accusations of UCI complicity and cover-up in Armstrong's activities, denounced the American as an "opportunist".

"The Tour de France gets under way this weekend, so he's decided to attack the Tour de France at this precise moment and to attack the authorities," he added.

"Lance Armstrong is someone who only thinks about himself."

Five-time Tour winner also Bernard Hinault reacted angrily to Armstrong's comments, calling for an end to claims that all cyclists were "thugs and druggies".

"It depresses me to hear all this," he told BFM TV, suggesting that other sports were also implicated.

"Stop saying it's cultural for God's sake. It's impossible. There are plenty of young riders who've had dope tests and not tested positive. It's constant suspicion," he added.

Hinault on Thursday lashed out at claims that his fellow French cyclist Laurent Jalabert took EPO on the scandal-hit 1998 Tour, claiming that people wanted to "kill" the race.