USADA chief Tygart: Armstrong lied to Oprah

US Anti-Doping Agency chief Travis Tygart says Lance Armstrong lied in his confessional interview with Oprah Winfrey, and the shamed cyclist has until February 6 to "cooperate fully" if he wants to lessen his life ban.

In an excerpt of an interview with the CBS network to air in full on Sunday, Tygart said Armstrong lied about several key points -- including his claim that he raced clean in his comeback in 2009 and 2010.

Tygart said he has written to the shamed cyclist and offered him a deadline of February 6 to "cooperate fully and truthfully" in exchange for a possible lessening of his lifetime ban from sports.