Lawyers for Lance Armstrong fired a scathing shot at the U.S. government on Tuesday, asking a federal judge to dismiss a $120 million whistleblower lawsuit that accused him, and others, of defrauding his former team's sponsor, the U.S. Postal Service.

Mr. Armstrong, who was stripped of his seven Tour de France titles last year, admitted in January that he used performance-enhancing drugs to win the races. He lost all of his major sponsorship deals and is banned for life from competition.

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