USADA branded Armstrong a dope cheat a day after the 40-year-old Texan said he wouldn't pursue a bid to clear himself of charges that he used performance enhancing drugs to win cycling's most prestigious race from 1999 to 2005.

The agency laid out five rule violations for which Armstrong has been sanctioned, saying the cancer survivor who became a hero to millions took part in a systematic doping conspiracy with his then US Postal Service team.

It said that, as Armstrong has dropped out of an arbitration process, he "has received a lifetime period of ineligibility and disqualification of all competitive results from August 1, 1998 through the present".

Along with his celebrated haul of Tour titles Armstrong stands to lose the Olympic bronze medal he won in 2000 along with other race titles, prize money and other awards.

Armstrong, the only cyclist to win the Tour de France more than five times, had long vehemently denied doping accusations.

But on Thursday he said had grown weary of the fight and the strain it had put on his personal and professional life.

"There comes a point in every man's life when he has to say 'enough is enough.' For me, that time is now," he said in a statement.

The International Cycling Union, the sport's governing body based in Aigle, Switzerland, had been fighting USADA for jurisdiction of Armstrong's case and could launch an appeal or fail to recognise the move.

However, USADA's statement made it clear they believe the UCI is bound by the World Anti-Doping Code to follow through on the sanctions.

"Because Mr. Armstrong could have had a hearing before neutral arbitrators to contest USADA's evidence and sanction and he voluntarily chose not to do so, USADA's sanction is final," the agency's statement said.

Armstrong, who has branded the USADA investigation "an unconstitutional witch hunt," had gone to court in a bid to block the agency's proceedings.

But on Monday a federal judge in his hometown of Austin dismissed his lawsuit, leaving Armstrong until midnight on Thursday to tell USADA whether or not he would seek arbitration.

"I have been dealing with claims that I cheated and had an unfair advantage in winning my seven Tours since 1999," Armstrong said Thursday night.

"The toll this has taken on my family, and my work for our foundation and on me leads me to where I am today - finished with this nonsense."

USADA maintains that Armstrong used banned substances - including the blood-booster EPO, steroids and blood transfusions - dating back to 1996, and said 10 of his former team-mates were ready to testify against him.

If the UCI confirms the move, it faces a potential headache of choosing new winners for the seven disputed tours, as a number of cyclists who finished behind the American have also been implicated in doping scandals.

Indeed, Armstrong has argued that at least some of the witnesses who have implicated him can't be trusted as they are themselves admitted dope cheats.

Former teammate Floyd Landis, who finally admitted doping years after he was stripped of his 2006 Tour de France title, accused Armstrong of systematic doping, helping trigger a federal government probe of Armstrong and others.

That investigation ended in February with no criminal charges brought, but it apparently provided further impetus to USADA's probe of the cyclist.