GENEVA—Lance Armstrong was officially stripped of his titles Monday by cycling's governing body in the latest chapter in the doping allegations against the seven-time Tour de France champion.

The International Cycling Union, the sport's governing body known as UCI, acted following a damning report by U.S. antidoping authorities that said Mr. Armstrong was at the center of "a massive team doping scheme, more extensive than any previously revealed in professional sports history."

The...