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, which will air in full on "60 Minutes" 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.
The USADA chief also told CBS that Armstrong's vehement claim that he didn't use performance-enhancing drugs when he came out of retirement to race in the Tour de France in 2009 and 2010 is "just contrary to the evidence".
Tygart reiterated the claims outlined in the report issued last year by USADA, on which the agency based its lifetime ban of Armstrong and the forfeiture of all of his cycling results from August 1998.
According to Tygart, expert reports based on the variation of Armstrong's blood values in those years make it "one to a million chance that it was due to something other than doping".
Armstrong, who vehemently denied doping during his career, admitted publicly for the first time to talk show diva Winfrey that he used an array of banned drugs in claiming seven Tour de France triumphs from 1999-2005.
Tygart says Armstrong would lie about his comeback because under the statute of limitations for criminal fraud, he would still be open to prosecution for fraud.
Tygart also took issue with Armstrong's claim that his favored drug cocktail of blood-boosting EPO, blood transfusions and testosterone included just a small amount of EPO.
"He used a lot of EPO," Tygart told "60 Minutes".
In the second segment of his interview with Winfrey, which aired over two nights on January 18-19, the 41-year-old Armstrong said he wants to compete again in sport -- suggesting he could see himself racing in the Chicago Marathon.
Noting that cyclists who implicated themselves in testifying against him had received lesser punishments, Armstrong said he wasn't sure he deserved a "death penalty" of a lifetime ban.
Tygart had responded immediately after Armstrong's first confession aired last week, saying Armstrong had to testify under oath about his doping to have any hope of reducing his sanction.
"His admission that he doped throughout his career is a small step in the right direction," Tygart said shortly after the interview aired.
"But if he is sincere in his desire to correct his past mistakes, he will testify under oath about the full extent of his doping activities."