COLORADO SPRINGS, Colorado (AFP) - United States Anti-Doping Agency (USADA) chief executive Travis Tygart on Thursday called Lance Armstrong's admission of doping "a small step in the right direction", for the shamed cyclist.

"Tonight, Lance Armstrong finally acknowledged that his cycling career was built on a powerful combination of doping and deceit," said Mr Tygart, who guided the USADA probe that led to Armstrong being stripped of the record seven Tour de France titles and banned from the sport.

Armstrong had previously dubbed USADA's investigation a "witch-hunt" and accusing Mr Tygart and his colleagues of pursuing a "vendetta" against him and going so far as a lawsuit questioning their jurisdiction.

Mr Tygart's brief statement made reference to none of that, nor did it address any details of Armstrong's confessions and which USADA charges Armstrong verified or challenged.

"His admission that he doped throughout his career is a small step in the right direction," Mr Tygart said.

"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."