London, June 16 : The sponsors of cycling champion Lance Armstrong have vowed to stand behind the seven-time Tour de France winner, even as Armstrong''s lawyers have started to challenge the new doping charges against him.

Armstrong's sponsors have shown support for him, including apparel makers Nike and Oakley and beermaker Anheuser-Busch.

"Our relationship with Lance remains as strong as ever," Sports24 quoted Nike as saying in statement, while Oakley reiterated the same in its statement, "As always we believe in Lance".

"Our partnership with Lance remains unchanged," Anheuser-Busch US Marketing Vice President Paul Chibe said.

The US Anti-Doping Agency (USADA) brought doping conspiracy charges against Armstrong on Wednesday and has not responded to the letters from Armstrong attorneys, which seek details of the evidence that 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's spokesperson Mark Fabiani, was reported as saying.

Armstrong has another week to make a written response to the charges under the guidelines of USADA investigations, after which 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, in which Armstrong allegedly cheated using drugs, ranging from the abuse of erythropoietin (EPO) through to methods such as blood transfusions and saline infusions. (ANI)