(CNN) -- Champion cyclist Lance Armstrong said Wednesday the U.S. Anti-Doping Agency intends to "dredge up discredited" doping allegations against him in a bid to strip him of his seven Tour de France victories.
The Washington Post said it received a copy of a 15-page agency letter sent Tuesday to Armstrong and several others. As a result of the allegations, Armstrong was immediately banned from competing in triathlons, a sport he took up after retiring from professional bicycling, the newspaper reported on its website.
Armstrong, as he has in the past, said he has never engaged in doping.
"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 on his website. "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."
Justice Department prosecutors in February said they closed a criminal investigation after reviewing allegations against Armstrong. They had called witnesses to a federal grand jury in Los Angeles, but they apparently determined they lacked evidence to bring a charge that Armstrong used performance-enhancing drugs.
Armstrong was accused of using such drugs by other riders, but never failed a drug test.
"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 Wednesday.
According to the Post, the U.S. Anti-Doping Agency alleged it collected blood samples from Armstrong in 2009 and 2010 that were "fully consistent with blood manipulation including EPO use and/or blood transfusions." The allegations were previously unpublicized, according to the Post.
The letter says Armstrong and five former cycling team associates engaged in a doping conspiracy from 1998 to 2011, the Post reported. Riders will testify that Armstrong used EPO, blood transfusions, testosterone and masking agents, and that he distributed and administered drugs to other cyclists from 1998 to 2005, the Post quoted the letter as saying.
In a statement obtained by CNN, U.S. Anti-Doping Agency CEO Travis T. Tygart said the five other people, formerly associated with the U.S. Postal Service pro cycling team, are three team doctors and two team officials. The letter included written notice of alleged anti-doping rule violations, Tygart said
"USADA only initiates matters supported by the evidence," Tygart said. "We do not choose whether or not we do our job based on outside pressures, intimidation or for any reason other than the evidence." All named individuals are presumed innocent until proven otherwise, he added.
His statement did not mention anything about Armstrong's status as a triathlete.
According to its website, the quasi-government agency is recognized as the official anti-doping agency for Olympic, Pan American and Paralympic events in the United States.
Armstrong lashed out at the organization, saying it has "self-written rules" and that it punishes first and adjudicates the facts later.
Armstrong has been dogged by allegations of drug abuse in recent years, with compatriot Floyd Landis -- who was found guilty of doping in the 2006 Tour de France, resulting in him being stripped of the title -- making a series of claims last year.
Armstrong came out fighting once again in May 2011 in the face of fresh allegations made on the CBS News "60 Minutes" show by another American, Tyler Hamilton.
In the CBS interview, Hamilton -- who retired in 2009 after twice testing positive himself -- says he first saw Armstrong use blood boosting substance EPO in 1999, the year of his first Tour de France victory.
"I saw it in his refrigerator," Hamilton told the American news program. "I saw him inject it more than one time like we all did, like I did many, many times."
On his Twitter page, Armstrong at the time said he never failed a drug test.
CNN's Terry Frieden and Jason Durand contributed to this report.