Justice Department prosecutors said Friday that they are closing a criminal investigation of champion cyclist Lance Armstrong without filing charges that he used performance-enhancing drugs.

A statement from the U.S. attorney in Los Angeles said the seven-time Tour de France winner will not be charged, but did not explain the reasons for the decision.

Armstrong has consistently denied doping. He was accused of using performance-enhancing drugs by other riders, but never failed a drug test.

Late Friday, he released a statement in which he said he was "gratified" to learn that prosecutors are closing their investigation.

"It is the right decision and I commend them for reaching it. I look forward to continuing my life as a father, a competitor and an advocate in the fight against cancer without this distraction," Armstrong said.

Prosecutors called witnesses to a federal grand jury in Los Angeles as they investigated the case, but they apparently determined that they lacked evidence to bring a charge.

In May 2011, Armstrong once again denied claims from a former teammate that he used drugs during his cycling career.

Armstrong has been dogged by allegations of drugs abuse in recent years with compatriot Floyd Landis -- who was found guilty of doping in the 2006 Tour de France resulting in him being stripped of the title -- making a series of claims last year.

Armstrong came out fighting once again in May, in the face of fresh allegations made on the CBS News "60 Minutes" show by another American Tyler Hamilton.

On his Twitter page, Armstrong said at the time: "I have had a 20-year career, 500 drug controls worldwide, in and out of competition, and never a failed test. I rest my case."

In the CBS interview, Hamilton -- who retired in 2009 after twice testing positive himself -- says he first saw Armstrong use blood boosting substance EPO in 1999, the year of his first Tour de France victory.

"I saw it in his refrigerator," Hamilton told the American news program. "I saw him inject it more than one time like we all did, like I did many, many times."

Hamilton added: "Armstrong took what we all took -- the majority of the peloton took. There was EPO, testosterone, blood transfusions."

Meanwhile, Armstrong's lawyer Mark Fabiani blasted the "60 Minutes" report, releasing a statement saying: "Hamilton is actively seeking to make money by writing a book.

"He has completely changed the story he has always told before so that he could get himself on "60 Minutes" and increase his chances with publishers."

Fabiani continued: "Greed and a hunger for publicity cannot change the facts: Lance Armstrong is the most tested athlete in the history of sports: He has passed nearly 500 tests over 20 years of competition."