By Corrie MacLaggan

AUSTIN, Texas (Reuters) - Cyclist Lance Armstrong confessed to using performance-enhancing drugs in an interview on Monday with Oprah Winfrey, USA Today reported.

Although American media had widely speculated that Armstrong would admit to cheating in the interview, neither Winfrey nor Armstrong confirmed the report, in which the newspaper cited an anonymous source.

"We are not confirming any specific details regarding the interview at this time," a spokesman for Oprah's network OWN told Reuters.

Armstrong has always vehemently denied using performance-enhancing drugs and had never tested positive to a doping test.

The report did not say which drugs Armstrong admitted to using and the American's attorney and his spokesman did not immediately respond to requests for comment.

Oprah, on Twitter, offered little more herself, other than to say Armstrong came prepared for the interview, which will be broadcast on Thursday.

"Just wrapped with @lancearmstrong More than 2 1/2 hours. He came READY," Winfrey tweeted.

But the television host did confirm she would appear on CBS television on Tuesday morning to talk about the interview.

CBS reported Armstrong, a former cancer survivor who went on to become the greatest cyclist the world has seen, had indicated he may be willing to testify against others involved in illegal doping and was in talks about repaying part of the taxpayer money he earned during his career.

The unconfirmed reports about his admissions followed confirmation that Armstrong apologized to the staff of the cancer foundation he started because of the damage he had caused.

"He had a private conversation with the staff, who have done the important work of the foundation for many years," said Livestrong Foundation spokeswoman Katherine McLane.

"It was a very sincere and heartfelt expression of regret over any stress that they've suffered over the course of the last few years as a result of the media attention," she said.

Shortly after, Armstrong joined his legal team to meet with Winfrey for an interview described as "no-holds-barred".

The interview was supposed to take place at Armstrong's home in Texas but was switched to a hotel in downtown Austin after news crews camped outside his house before dawn.

But an October report from the U.S. anti-doping body USADA cited Armstrong's involvement in what it characterized as the "most sophisticated, professionalized and successful doping program that sport has ever seen," involving anabolic steroids, human growth hormone, blood transfusions and other doping.

Less than two weeks later, Armstrong's seven Tour de France victories were nullified and he was banned from cycling for life after the International Cycling Union ratified the USADA's sanctions against him.

(Additional reporting by Frank Pingue, writing by Julian Linden, editing by Philip Barbara)