[[CNN) -- The U.S. Anti-Doping Agency said early Friday it will strip Lance Armstrong of his seven Tour de France titles and impose a lifetime ban, a move that came just hours after the cyclist announced he would no longer fight charges of illegal doping.

A formal announcement by the USADA is expected later in the day, "but his choosing not to contest the charges means that there will be a lifetime ban and a loss of all results beginning from August 1, 1998," agency spokeswoman Annie Skinner told CNN in an emailed statement.

Even so, there is a question about whether the USADA -- a quasi-government agency recognized as the official anti-doping agency for Olympic, Pan American and Paralympic sports in the United States -- has the authority to take action against Armstrong.

The International Cycling Federation, whom Armstrong has said should be the arbiter in his case, has opposed the American agency's actions by claiming it has jurisdiction. That position has been recently backed by USA Cycling, the official cycling organization recognized by the U.S. Olympic Committee.

The USADA's action followed news late Thursday that Armstrong was calling it quits in his battle to end an investigation by the USADA.

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

The USADA has accused Armstrong of using, possessing, trafficking and giving to others performance-enhancing drugs, as well as covering up doping violations.

Armstrong, who has long denied allegations of illegal doping, made his announcement after losing a legal bid Monday to halt the anti-doping agency's legal case against him, which came more than a year after his retirement from cycling and subsequent move to triathlon competitions.

The 40-year-old, who fought back from testicular cancer to win cycling's biggest race from 1999 to 2005, has described himself as the "most tested athlete in the world." He retired twice from cycling -- first in 2005, for four years, and again in 2011.

Armstrong has never been convicted of any doping charges.

The USADA alleges he took steroids throughout his career, saying it has testimony from former teammates to support the charges. It has refused to reveal who provided the evidence.

Although USADA officials had not seen Armstrong's statement late Thursday, its chief executive called it "a sad day for all of us who love sport and our athletic heroes."

"This is a heartbreaking example of how the win-at-all costs culture of sport, if left unchecked, will overtake fair, safe and honest competition, but for clean athletes, it is a reassuring reminder that there is hope for future generations to compete on a level playing field without the use of performance-enhancing drugs," CEO Travis T. Tygart said in a statement.

Armstrong called Tygart's investigation an "unconstitutional witch hunt."

"I have been dealing with claims that I cheated and had an unfair advantage in winning my seven Tours since 1999. Over the past three years, I have been subjected to a two-year federal criminal investigation followed by Travis Tygart's unconstitutional witch hunt. 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," he said.

If found guilty by the USADA, Armstrong faced a lifetime ban from all sports covered by the World Anti-Doping Agency.

"Today I turn the page. I will no longer address this issue, regardless of the circumstances," Armstrong said Thursday.

"I will commit myself to the work I began before ever winning a single Tour de France title: serving people and families affected by cancer, especially those in underserved communities."

Armstrong has been dogged by doping allegations in recent years, with compatriot Floyd Landis -- who was stripped of his 2006 Tour de France title after failing a drug test -- making a series of claims last year.

Armstrong came out fighting in May 2011, in the face of fresh allegations made on CBS News' "60 Minutes" show by another American, Tyler Hamilton. In the CBS interview, Hamilton -- who retired in 2009 after twice testing positive himself and who, earlier this month, was stripped of his 2004 gold medal by the International Olympic Committee due to doping -- said he first saw Armstrong use EPO in 1999.

EPO, or erythropoietin, boosts the number of red blood cells, which carry oxygen to the muscles.

Armstrong has said in court documents that he has never had "a single positive test" in the 500 to 600 drug tests he's taken in his more than two decades in cycling.

"From the beginning, however, this investigation has not been about learning the truth or cleaning up cycling, but about punishing me at all costs. I am a retired cyclist, yet USADA has lodged charges over 17 years old despite its own 8-year limitation," Armstrong said in Thursday's statement.

In February, Justice Department prosecutors said they closed a criminal investigation after reviewing allegations against Armstrong. They had called witnesses to a federal grand jury in Los Angeles, but apparently determined they lacked evidence to bring a charge that Armstrong used performance-enhancing drugs.

In a June letter to Armstrong, a copy of which was obtained by CNN, the USADA said it collected blood samples from Armstrong in 2009 and 2010 that were "fully consistent with blood manipulation including EPO use and/or blood transfusions."

Armstrong sued the USADA to stop the investigation, arguing it did not have the right to prosecute him.

But a federal judge on Monday dismissed Armstrong's lawsuit after ruling the court did not have jurisdiction.

U.S. District Judge Sam Sparks acknowledged "the appearance of a conflict on the part of both organizations creates doubt the charges against Armstrong would receive fair consideration in either forum." But that doesn't mean federal courts should intervene, the judge said, adding "these matters should be resolved internally, by the parties most affected."

"If these bodies wish to damage the image of their sport through bitter infighting, they will have to do so without the involvement of the United States courts," Sparks said.