Lance Armstrong's lawyers have already started to challenge the new doping charges against him even as sponsors vow to stand behind the seven-time Tour de France cycling champion.

The US Anti-Doping Agency (USADA) brought doping conspiracy charges against Armstrong (pictured) on Wednesday and has not responded to letters from Armstrong attorneys seeking details of the evidence they claim to have against him.

"USADA has failed to respond to either of our two letters and so the answer is yes, they are refusing at this point to turn over any evidence," Armstrong spokesman Mark Fabiani told the Austin American-Statesman.

Armstrong has another week to make a written response to the charges under the guidlines of USADA investigations. After that an independent panel will consider the evidence and decide if the charges merit a hearing.

A 15-page letter from USADA detailed the agency claims, but it comes in the wake of the US Justice Department dropping its probe after two years of investigation without filing any charges against Armstrong.

While USADA cannot impose criminal penalties against Armstrong, it has asked that Armstrong be banned from any sport for life and would open the door for him to be stripped of the Tour de France victories he won from 1999-2005.

Armstrong, who has steadfastly denied any wrongdoing for years, has never tested positive for performance-enhancing drugs and called the USADA charges a "witch hunt" in a Twitter statement denouncing the move.

Armstrong's lawyers want drug test analysis from USADA on blood test results from Armstrong's 2009 and 2010 Tour de France runs, which the USADA says showed signs of the banned blood booster EPO.

There was no positive test from the race in either year involving samples from Armstrong.

USADA also claims to have testimony from 10 cyclists regarding Armstrong's actions.

The charges were enough to prompt Ironman triathlon officials to ban Armstrong from an event later this month in Nice, France. Armstrong had planned to compete in the World Ironman Championships in Hawaii in October.

The move comes as corporate sponsors offer shows of support for Armstrong, including apparel makers Nike and Oakley and beer-maker Anheuser-Busch.

"Our relationship with Lance remains as strong as ever," Nike said, with Oakley adding, "As always we believe in Lance" in a statement.

"Our partnership with Lance remains unchanged," Anheuser-Busch US marketing vice president Paul Chibe said.

(China Daily 06/17/2012 page7)