WASHINGTON -- The Justice Department joined a lawsuit Friday against disgraced cyclist Lance Armstrong alleging that the former seven-time Tour de France champion concealed his use of performance-enhancing drugs and defrauded his longtime sponsor, the U.S. Postal Service.The lawsuit alleges that riders on the Postal Service-sponsored team, including Armstrong, knowingly violated their Postal Service agreements by regularly using banned substances and methods to enhance their performance."Lance Armstrong and his cycling team took more than $30 million from the U.S. Postal Service based on their contractual promise to play fair and abide by the rules -- including the rules against doping," said U.S. Attorney Ronald Machen, whose office is handling the case. "The Postal Service has now seen its sponsorship unfairly associated with what has been described as 'the most sophisticated, professionalized and successful doping program that sport has ever seen.'"In recent weeks, settlement discussions had been under way between the Justice Department and Armstrong's lawyers. A person familiar with the negotiations said Friday that the two sides are tens of millions of dollars apart on how much Armstrong should pay to settle the case.From 1996 through 2004, the Postal Service sponsored a professional cycling team run by Tailwind Sports Corp., and Armstrong was the lead rider. From 1999 to 2004, he won six consecutive Tour de France titles. The suit also said Johan Bruyneel, the team's manager, facilitated the use of performance-enhancing substances.The U.S. Anti-Doping Agency last month lobbied Attorney General Eric Holder for the Justice Department to join the lawsuit against Armstrong.Its CEO, Travis Tygart, said Friday, "USADA applauds today's action by the U.S. Department of Justice which holds promise for returning the many millions of federal dollars in ill-gotten gains generated by this fraud."It was USADA's investigative report in October that led to Armstrong being stripped of his medals.An Armstrong lawyer, Robert Luskin, said negotiations with the government failed because "we disagree about whether the postal service was damaged.""The Postal Service's own studies show that the service benefited tremendously from its sponsorship -- benefits totaling more than $100 million," Luskin said.The suit the Justice Department is joining was filed under seal in 2010 by former teammate Floyd Landis, who was stripped of his 2006 Tour de France title for doping. Under the False Claims Act, private citizens can act as whistle-blowers and sue to recover money they believe was obtained through fraud against the federal government. These suits remain under seal until the Justice Department decides whether it thinks there is enough merit in the case to take it over. The private whistle-blower receives a percentage of any money ultimately recovered.In his 2010 complaint, made public Friday, Landis gave a detailed account of what he alleged had been widespread use of performance-enhancing drugs by Armstrong and assistance from Bruyneel and others.During the 2002 Tour de France, Landis and Armstrong lay on opposite sides of a bed to receive re-infusions of a half-liter of blood each, Landis' complaint said.In Spain in 2003, the withdrawal of blood had left Landis in need of EPO -- a banned hormone that increases oxygen-carrying red blood cells. Landis said he went to Armstrong's apartment, where Armstrong gave him EPO.