The head of the United States Anti-Doping Agency Travis Tygart has insisted that disgraced cyclist Lance Armstrong took performance-enhancing drugs for his comeback in 2009 and 2010.

The 41-year-old, who admitted to doping throughout his career, has maintained that he was clean when he returned to the sport, but Tygart has claimed that there is evidence that the Texan cheated again when he came out of retirement.

"[That is] just contrary to the evidence," Tygart told CBS's 60 Minutes. "The evidence is clear. 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."

Armstrong was stripped of his seven Tour de France titles and issued with a lifetime ban following the revelations.