Although federal investigators in February closed a two-year investigation without bringing criminal charges, the U.S. Anti-Doping Agency has filed new doping charges that could strip the seven-time Tour de France winner of his victories in cycling's premier race.
Armstrong insists he is innocent.
"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. "Any fair consideration of these allegations has and will continue to vindicate me."
The move by USADA immediately bans him from competing in triathlons, which he turned to after he retired from cycling last year.
Armstrong has been dogged by doping allegations since his first Tour victory in 1999, but had hoped his fight to be viewed as a clean champion was finally won after federal prosecutors closed their probe. Armstrong has said the investigation took a heavy emotional toll and he was relieved when it ended.
But USADA officials insisted they would continue to pursue their investigation into Armstrong and his former teams and doctors, and notified him of the charges in a 15-page letter on Tuesday. Unlike federal prosecutors, USADA isn't burdened by proving a crime occurred, just that there was use of performance-enhancing drugs.
In its letter, USADA said its investigation included evidence dating to 1996. It also included the new charge that Armstrong blood samples taken in 2009 and 2010 are "fully consistent with blood manipulation including EPO use and/or blood transfusions." Armstrong came out of his first retirement to race in the Tour de France those two years.
Armstrong, who was in France training for a triathlon, dismissed the latest allegations as "baseless" and "motivated by spite."
Even though he last won the Tour seven years ago, the 40-year-old Armstrong remains a popular — if polarizing — figure, partly because of his charity work for cancer patients.
Since he first retired after the 2005 Tour de France, Armstrong has often said he was tired of fighting doping claims only to vigorously battle to clear his name. He spent millions assembling a legal team during the criminal investigation.
In the months since the criminal probe ended, Armstrong has said he would not worry about a USADA investigation and that he's done "wasting" time answering doping questions.
Anti-doping officials, however, kept pressing their case and finally laid out the charges in the letter.
The USADA letter, a copy of which was obtained by The Associated Press, accuses Armstrong of using and promoting the use of the blood booster EPO, blood transfusions, testosterone, human growth hormone and anti-inflammatory steroids. The letter doesn't cite specific examples, but says the charges are based on evidence gathered in an investigation of Armstrong's teams, including interviews with witnesses who aren't named.
USADA's letter said the agency was also bringing doping charges against Johan Bruyneel, manager of Armstrong's winning teams; team doctors Pedro Celaya and Luis Garcia del Moral; team trainer Pepe Marti, and consulting doctor Michele Ferrari.
No one answered the phone at the home of Ferrari in Ferrara, northern Italy. Ferrari's lawyer, Dario Bolognesi, said he was unaware of the USADA action and had no immediate comment.
Garcia del Moral's office told The AP in Spain that he would not comment on the charges. Celaya, who is currently on Radioshack's medical staff, was unreachable for comment.
Marti also has connections to another high-profile doping case. He was Alberto Contador's team coach through 2010, when the Spaniard was found to have used performance enhancing substances to win the Tour de France for a third time.
In February, Contador was stripped of his 2010 title after losing a drawn-out court battle with the International Cycling Union and World Anti-Doping Agency. The ruling came just three days after U.S. federal prosecutors dropped a doping investigation involving Armstrong. The American was a teammate of Contador during the Spaniard's 2009 Tour victory.
Contador's spokesman said the Spanish rider no longer worked with Marti and that their previous relationship was limited to being teammates.
"This is a coincidence of him (Contador) being on the teams for which he (Marti) worked," Jacinto Vidarte told The Associated Press. "It has nothing to do with what has happened. That period of when he was with the team is over."
Cycling's governing body, the International Cycling Union, which collected the 2009 and 2010 samples cited in the USADA letter, said it was not involved in the anti-doping group's investigation.
According to USADA's letter, more than 10 cyclists as well as team employees will testify they either saw Armstrong dope or heard him tell them he used EPO, blood transfusions, testosterone and cortisone from 1996 to 2005. Armstrong won the Tour de France every year from 1999-2005.
During their investigation, federal prosecutors subpoenaed Armstrong supporters and ex-teammates to testify in Los Angeles. One of the most serious accusations came during a "60 Minutes" interview when former teammate Tyler Hamilton said he saw Armstrong use EPO during the 1999 Tour de France and in preparation for the 2000 and 2001 tours.
Early in the criminal investigation, Armstrong attorney's accused USADA of offering cyclists a "sweetheart deal" if they would testify or provide evidence against Armstrong.
In a letter to USADA last week, Armstrong attorney Robert Luskin noted that USADA Chief Executive Officer Travis Tygart participated in witness interviews with federal investigator Jeff Novitzky during the criminal probe.
"It is a vendetta, which has nothing to do with learning the truth and everything to do with settling a score and garnering publicity at Lance's expense," Luskin wrote.
In a statement, Tygart said, "USADA only initiates matters supported by the evidence. We do not choose whether or not we do our job based on outside pressures, intimidation or for any reason other than the evidence."
Armstrong has until June 22 to file a written response to the charges. The case could ultimately go before an arbitration panel to consider evidence. The USADA letter said in that case a hearing should be expected by November.
Associated Press writers Joseph Wilson in Barcelona, Spain, and Victor L. Simpson in Rome contributed.