The U.S. Anti-Doping Agency brought formal doping charges against former cyclist Lance Armstrong in an action that could cost him his seven Tour de France titles, according to a letter sent to Armstrong and several others.

As a result of the charges, Armstrong has been immediately banned from competition in triathlons, a sport he took up after his retirement from cycling in 2011.

In the 15-page charging letter obtained by The Washington Post, USADA made previously unpublicized allegations against Armstrong, alleging it collected blood samples from Armstrong in 2009 and 2010 that were "fully consistent with blood manipulation including EPO use and/or blood transfusions." Armstrong has never tested positive.

In February, the U.S. Attorney's Office in Los Angeles ended a nearly two-year investigation into doping allegations involving Armstrong without bringing criminal charges. Armstrong's former teammates Floyd Landis and Tyler Hamilton cooperated with federal agents in that investigation and publicly accused Armstrong of doping.

USADA is the quasi-government agency that oversees anti-doping in Olympic sports in the United States. It is empowered to bring charges that could lead to suspension from competition and the rescinding of awards.

"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 released by his publicist. "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."

USADA's letter, dated June 12, alleges that Armstrong and five former cycling team associates engaged in a massive doping conspiracy from 1998 to 2011, and that "the witnesses to the conduct described in this letter include more than ten (10) cyclists."