MONTREAL (AFP) - Lance Armstrong must confess to doping under oath and aid the fight against cheating if he hopes to mitigate his life ban, World Anti-Doping Agency (Wada) director general David Howman said on Tuesday.

United States (US) talk show host Oprah Winfrey confirmed on Tuesday that the fallen cycling icon "came clean" on his use of performance enhancing drugs in an interview taped at his Austin, Texas, home on Monday.

The interview is to air in two parts on Winfrey's OWN cable network on Thursday and Friday.

"Wada has read with interest media reports suggesting a television 'confession' made by Lance Armstrong," Mr Howman said in a statement.

"While Wada encourages all athletes to come clean about any doping activities they have been involved with or know about, these details must be passed on to the relevant anti-doping authorities."

Armstrong lost his record seven Tour de France titles along with most of his other cycling achievements when the International Cycling Union (UCI) upheld the life ban meted out by the US Anti-Doping Agency last year.

The 41-year-old reportedly hopes a public confession could open the door to a return to competitive sport in marathons and triathlons.

"Only when Mr. Armstrong makes a full confession under oath - and tells the anti-doping authorities all he knows about doping activities - can any legal and proper process for him to seek any reopening or reconsideration of his lifetime ban commence," Mr Howman said.