The US Anti-Doping Agency has brought doping charges against champion Lance Armstrong that may cost him his record seven Tour de France titles, the cyclist said.
Armstrong has also been slapped with an immediate ban from competing in triathlons organised by the World Triathlon Corporation.
The 40-year-old said in a statement posted on his website that he has been informed of the pending action and strongly denied the allegations, claiming the USADA had a ''vendetta'' against him.
In a 15-page charging letter obtained by The Washington Post, the agency alleged it had collected blood samples from Armstrong in 2009 and 2010 that were ''fully consistent with blood manipulation including EPO use and/or blood transfusions."
The letter alleges that Armstrong, who won the Tour every year from 1999 to 2005 after surviving testicular cancer, used EPO, blood transfusions, testosterone, corticosteroids and masking agents, and that he distributed and administered drugs to others.
Cycling's world governing body, the International Cycling Union or UCI, said in a statement that it had been notified of USADA's probe but didn't identify any of the people involved.
The allegations have never been publicised before, and Armstrong has never tested positive.
Armstrong, who retired from professional cycling in February 2011 to focus on his cancer charity, has denied using banned performance-enhancing drugs.
"I have never doped, and, unlike many of my accusers, I have competed as an endurance athlete for 25 years with no spike in performance, passed more than 500 drug tests and never failed one," Armstrong said in a statement.
"That USADA ignores this fundamental distinction and charges me instead of the admitted dopers says far more about USADA, its lack of fairness and this vendetta than it does about my guilt or innocence. Any fair consideration of these allegations has and will continue to vindicate me."
It follows a two-year investigation by the US Attorney's Office in Los Angeles into doping allegations which ended in February without any charges being filed against Armstrong.
Armstrong's former teammates Floyd Landis and Tyler Hamilton cooperated with federal agents in that investigation and publicly accused Armstrong of doping.
''These are the very same charges and the same witnesses that the Justice Department chose not to pursue after a two-year investigation,'' Armstrong said.
''These charges are baseless, motivated by spite and advanced through testimony bought and paid for by promises of anonymity and immunity.''
The US Anti-Doping Agency is a quasi-government agency that oversees anti-doping in Olympic sports in the US, according to the Washington Post.
It can lay charges that could lead to suspension from competition and the rescinding of awards, however it does not have authority to bring criminal charges.
In the letter obtained by the newspaper, dated June 12, Armstrong and five former cycling team associates - three doctors including Italian physician Michele Ferrari, one trainer and team manager Johan Bruyneel- are accused of engaging in a large doping conspiracy from 1998-2011.
The agency alleges in the letter that the "witnesses to the conduct described in this letter include more than ten (10) cyclists.
All of the six, including trainer Pepi Marti of Switzerland and doctors Pedro Celaya of Luxembourg and Luis Garcia del Moral of Spain, face competition bans, according to the Washington Post.
"These charges are a product of malice and spite and not evidence," Armstrong's attorney Robert D. Luskin told the Washington Post.
"Nothing else explains the fact ... they allege an overarching doping conspiracy among four teams over 14 years and Lance is the only rider that gets charged."
Mr Luskin told the Washington Post that the agency sent Armstrong a letter last week asking him to meet with anti-doping officials. Armstrong declined, believing the agency was not interested in his testimony but rather a confession.
The letter further alleges that Martial Saugy, the director of an anti-doping lab in Switzerland, stated that Armstrong's urine sample results from the 2001 Tour of Switzerland indicated EPO use.
"Multiple witnesses" said Armstrong told them he had the test result covered up, a charge he has denied.
Saugy told The Washington Post last year that Armstrong's sample was merely "suspicious," a designation that meant it could not be called positive.
While further analysis with modern methods might bring clarity, Saugy said the sample no longer existed.
US Anti-Doping Agency chief executive Officer Travis Tygart could not be immediately reached to comment.
Armstrong has taken up competition in ironman triathlons since his retirement from cycling and was due to compete in the Ironman France in Nice on June 24.
- The Age