Armstrong uses Twitter to announce final Tour

Seven-time Tour de France winner Lance Armstrong announced on his Twitter web site that this year's Tour with his RadioShack team-mates will be his final one.

"And yes, this will be final Tour de France. It's been a great ride. Looking forward to three great weeks," the 38-year-old American wrote.

Realizing his tweet included some mistakes Armstrong then re-tweeted, "Doh, sorry, meant "my" final Tour."

On Saturday in Belgium, Armstrong will lead team RadioShack to begin his bid for an eighth Tour de France title.

The announcement comes just one month after the Texan found himself embroiled in new doping allegations, dismissing accusations levelled by his former team-mate Floyd Landis.

Landis, who was stripped of his 2006 Tour de France title after a positive drug test, pointed the finger at numerous cyclists, including Armstrong, and said that doping was intrinsic at the elite level of the sport.

Armstrong was quick to attack Landis's credibility.

Armstrong successfully beat cancer in 1998 to go on and win seven consecutive yellow jerseys from the world's toughest bike race in 1999-2005. He returned to the sport last year after a three-year 'retirement'.

Armstrong placed third at the 2009 Tour.