Washington, Jan 28 (IANS/EFE): The head of the US Anti-Doping Agency accused Lance Armstrong of lying during an interview earlier this month with Oprah Winfrey, in which the former cyclist acknowledged using performance-enhancing drugs for most of his career.

In an interview with CBS on the show "60 Minutes", extracts of which were released Saturday, Travis Tygart said the former cyclist - despite finally coming clean about his PED use for the first time - lied about several key points during the Jan 14 interview with the TV talk show host.

The USADA director also said he has sent a letter to Armstrong giving him until Feb 6 to fully cooperate in the investigation into his doping in exchange for a possible reduction in his lifetime suspension from all sports that adhere to the World Anti-Doping Agency code.

Tygart said Armstrong lied when he told Winfrey that the last time he used PEDs was in 2005 and that he was not a heavy user of the blood-booster EPO.

Those statement are not true and his blood tests in 2009 and 2010 - when Armstrong made a comeback - prove that, Tygart, who has been investigating Armstrong for years, said.

"His blood tests in 2009, 2010 - expert reports based on the variation of his blood values - from those tests, one to a million chance that it was due to something other than doping," the USADA chief said.

"He used a lot of EPO. You look at the '99 Tour de France samples and they were flaming positive, the highest that we've ever seen," Tygart added.

The USADA chief also contradicted the former cyclist's assertion that he did not pressure the fellow members of his US Postal Service Pro Cycling Team to dope.

"He was the boss. One of the ringleaders of a conspiracy that has deceived millions of fans and competitors," Tygart said.

Armstrong, a cancer survivor, was stripped last year of all seven of the Tour de France titles he won consecutively from 1999 to 2005 after refusing to defend himself from doping allegations compiled by USADA.

The International Cycling Union, or UCI, decided in October not to award the titles to the second-place finishers of those races, a move that lends credence to Armstrong's contention that he used PEDs as part of a larger doping culture in cycling.

The former cyclist, in fact, told Winfrey that he does not think any cyclist could have captured the Tour de France in the years he won the race and that he believes he was competing on a "level playing field".

Armstrong has lost lucrative endorsement contracts as a result of the scandal and in October he stepped down from the board of directors of the cancer-fighting Livestrong Foundation he founded in 1997.