USADA Chief executive Travis Tygart is confident the doping body can continue its investigation to clean up cycling without the help of Lance Armstrong.

The disgraced cyclist is not willing to testify under oath to USADA officials after admitting to doping during each of his seven Tour de France wins in a interview with Oprah Winfrey last month.

USADA had given the disgraced cyclist a two-week extension to participate with investigators, having initially been given until 6 February to confess all under oath.

And while the American's attorney Tim Herman stated Armstrong is willing to "co-operate fully", he "will not participate in USADA's efforts to selectively conduct American prosecutions that only demonise selected individuals".

The agency revealed last year that 41-year-old had led "the most sophisticated, professionalised and successful doping programme sport has ever seen" and Tygart is determined to move on from Armstrong.

"We have provided Mr Armstrong several opportunities to assist in our ongoing efforts to clean up the sport of cycling," Tygart said in a statement.

"Following his recent television interview, we again invited him to come in and provide honest information, and he was informed in writing by the World Anti-Doping Agency (WADA) that this was the appropriate avenue for him if he wanted to be part of the solution.

"Over the last few weeks he has led us to believe that he wanted to come in and assist USADA, but was worried of potential criminal and civil liability if he did so.

"We learned from the media that Mr Armstrong is choosing not to come in and be truthful and that he will not take the opportunity to work toward righting his wrongs in sport.

"At this time we are moving forward with our investigation without him and we will continue to work closely with WADA and other appropriate and responsible international authorities to fulfil our promise to clean athletes to protect their right to compete on a drug-free playing field."

An agreement appeared close when the USADA stated Armstrong wanted to "assist in the effort to clean up the sport of cycling" when they agreed to an extension, although those hopes have been dealt a blow with the release of his attorney's statement.

"Lance is willing to cooperate fully and has been very clear: he will be the first man through the door, and once inside will answer every question, at an international tribunal formed to comprehensively address pro cycling, an almost exclusively European sport," said the statement.

"We remain hopeful that an international effort will be mounted, and we will do everything we can to facilitate that result.

"In the meantime, for several reasons, Lance will not participate in USADA's efforts to selectively conduct American prosecutions that only demonise selected individuals while failing to address the 95 per cent of the sport over which USADA has no jurisdiction."