The first of a two-part exclusive Armstrong interview aired on US television and online Thursday evening. Winfrey - one of the United States' most prominent television personalities - began the discussion with yes and no questions aimed at eliciting the truth about Armstrong's doping history.

Armstrong admitted to using performance-enhancing drugs in each of his seven Tour de France victories since from 1999 to 2005. He confessed to having undergone blood transfusions, and taking the blood-booster EPO, as well as testosterone, cortisone and human growth hormone, to enhance his performance.

"There's no true justification [for my doping]," said Armstrong.

The internationally-known athlete said he was confessing now because he wanted to acknowledge his wrongdoing and to apologize.

"I don't know that I have a great answer [for why I'm confessing now]. This is too late. It's too late for probably most people. And that's my fault. I view this situation as one big lie that I repeated a lot of times."

Armstrong: 'It's inexcusable'

Over the course of the hour and a half broadcast on Thursday, Winfrey posed questions regarding the nature of his deceit, often asking him how in felt in retrospect.

He attributed his use of banned substances primarily to a "win-at-all-costs attitude" that his fight against cancer had heightened. Armstrong said he tried to bully whistleblowers who had accused him of using performance enhancing substances, by fighting back publicly and maintaining an image as a clean cyclist.

Armstrong, 41, never failed a drug test during his career, but witness testimony, including from former teammates, eventually led to an investigation into an elaborate doping system and his eventual downfall. Amid public pressure, the disgraced cyclist stepped down from his cancer foundation, Livestrong, in October.

In December, the champion cyclist declined to appeal a ruling that banished his name from the record books for the years that comprised the second phase of his career after beating testicular cancer in 1998. The International Cycling Union announced it bans earlier the same month.

He wasn't afraid of getting caught, nor did he feel like he had cheated at the time, he said.

Armstrong categorically denied forcing team-mates to dope. He maintained that he stopped doping after his last Tour de France victory in 2005, and that his third-place finish in 2009 was achieved legally.

He has since been stripped of all Tour de France titles, as well as his bronze medal from the Sydney Olympics in 2000.

"[My supporters] they have every right to feel betrayed. And it's my fault. I'll spend the rest of my life trying to earn back trust and apologize to people for the rest of my life."

The second part of the interview is scheduled to broadcast on Friday evening in the US.

kms/jr (AFP, dpa)