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Lance Armstrong (search) juggled controversy and ceremony Tuesday, promising to take action against "absolutely untrue" doping accusations and announcing a new sponsor.

Just 2½ weeks before he begins his attempt to win an unprecedented sixth consecutive Tour de France (search), Armstrong strongly denied claims by a former assistant in a new book. The assistant says Armstrong once asked her to dispose of used syringes and to give him makeup to conceal needle marks on his arms.

"I can absolutely confirm that we don't use doping products," Armstrong said at a news conference at the headquarters of Discovery Communications, which will begin sponsoring his team next year.

"This is not the first time I've lived through this. I heard it in 1999. I heard it in 2002, again in 2003. It happens all the time."

Armstrong said he usually ignores such claims but decided he had had enough. He also said he was frustrated to have to deal with a distraction so close to the Tour de France.

"We're sick and tired of these allegations and we're going to do everything we can to fight them," he said. "They're absolutely untrue."

The allegations took some of the shine away from the announcement of a three-year, multimillion-dollar deal with Discovery, which will replace the U.S. Postal Service as the sponsor of Armstrong's team. The prospect of not having a sponsor left the 32-year-old Armstrong contemplating retirement, but now he says he'll ride in next year's Tour de France and possibly beyond.

"I just didn't want to go away," said Armstrong, who was accompanied by his girlfriend, rocker Sheryl Crow. "I love what I do. I still love the bike."

The latest accusations appear in the French-language book "L.A. Confidential, the Secrets of Lance Armstrong" by David Walsh (search) and Pierre Ballester (search).

The heart of the accusations come from Emma O'Reilly, who worked for several years as Armstrong's masseuse, physical therapist and personal assistant. The book contends Armstrong asked O'Reilly to dispose of a black bag containing used syringes after the Tour of the Netherlands in 1998. O'Reilly said she did not know what was in the syringes, according to the book.

Armstrong said Tuesday he and O'Reilly had a "very good working relationship," but that she was fired because of "inappropriate" issues that had arisen within the team.

"Even as evil as this thing has come out to be, it's not going to be my style to attack her. ... I did not work with her very much," Armstrong said. "This is the first that I've heard from her in years and years. ... It does add up to a little bit of stress, but I've got to tell you when I go home, I'm not thinking about this. I'm thinking about winning the Tour."

Armstrong's lawyers said they were starting libel proceedings in France and Britain against Walsh and Ballester, as well as the book's publishers and publications that reprinted excerpts from the book, which hit Paris stores on Tuesday. Excerpts were published in France's L'Express magazine Monday.

Asked if he will also seek action against people named in the book, Armstrong said: "Right now we're talking about authors and publishers and papers and magazines that have excerpted the stuff, but we won't discriminate."

Co-author Walsh offered an explanation of the book in an interview with the International Herald Tribune.

"It's all circumstantial evidence," Walsh said. "We don't actually prove anything. We just set out the facts and let the reader decide for himself who's telling the truth. But we do give names for every accusation."