WASHINGTON: The US Anti-Doping Agency has brought formal doping charges against seven-time Tour de France winner Lance Armstrong, the Washington Post reported on Wednesday.

According to the newspaper, the action was outlined in a letter sent to Armstrong and several others and could cost the Texan his titles in the world's premier cycle race.

The Post reported that in the letter, USADA 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.”

According to the Post, which obtained a copy of the letter, USADA claims it has witnesses to the fact that Armstrong and five former cycling team associates – including Italian doctor Michele Ferrari and cycling team manager Johan Bruyneel – engaged in a doping conspiracy from 1998-2011.

USADA officials could not immediately be reached for comment on Wednesday.

Armstrong, who won the Tour de France from 1999-2005, and used his fame to fuel his charitable work for cancer awareness, has vehemently denied using performance-enhancing drugs during his cycling career.

He has never tested positive, but has been publicly accused by former teammates Floyd Landis and Tyler Hamilton of cheating.

In February, US prosecutors dropped an investigation into Armstrong and other cyclists without bringing criminal charges.

At the time USADA said it continued to investigate allegations of doping in cycling and hoped to have access to the information gathered in the criminal probe.

“Unlike the US Attorney, USADA's job is to protect clean sport rather than enforce specific criminal laws,” USADA chief executive Travis Tygart said in February.

“Our investigation into doping in the sport of cycling is continuing and we look forward to obtaining the information developed during the federal investigation.”