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The US Anti-Doping Agency said Thursday it would ban cyclist Lance Armstrong for life and strip him of his Tour de France wins.

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Armstrong on Thursday night dropped any further challenges to USADA’s allegations that he took performance-enhancing drugs.

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Armstrong had an unprecedented winning streak at the Tour de France, taking the title from 1999 to 2005.

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Armstrong, here in 2005 with Johan Bruyneel, sporting director of the Discovery team, became the sport's most popular figure.

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The USADA has maintained that Armstrong has used banned substances as far back as 1996.

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In a statement Thursday, Armstrong called the USADA investigation an ‘‘unconstitutional witch hunt.’’