Armstrong hits back at Landis over doping claims

Lance Armstrong fired back at former team mate Floyd Landis, who has publicly accused him of using performance enhancing drugs, following reports he is now working with law enforcement agencies.

Armstrong's lawyers issued a statement on the cyclist's team's website countering Landis' claims that Armstrong cheated during his seven Tour de France wins.

In the statement, Armstrong's lawyers posted a series of private emails which they claimed are between Landis, his personal doctor and cycling officials and sponsors.

"Even a superficial review reveals a troubling, angry and misplaced effort at retribution by Landis for his perceived slights," the statement said.

"While these types of repeated, tired and baseless accusations against Lance have been proven false in the past, it is quite regrettable, but telling, that so many in cycling are now attacked by a bitter and scorned Landis who, quite simply, has zero credibility."

The posting of the emails came a day after Landis, who was stripped of his 2006 Tour de France win, confessed to using blood-boosting drugs after pleading his innocence for years.

Landis also pointed the finger at Armstrong in emails he sent to media organisations, saying he had witnessed him using illegal drugs.

Armstrong, who has never failed a doping test but has long been accused of wrongdoing by critics and opponents, strongly denied the claims.

Doping and sporting authorities have asked Landis to provide evidence to back up his claims while the Wall Street Journal reported on Friday that Landis is now cooperating with the US criminal unit that investigated several high-profile athletes, including disgraced Olympic sprint champion Marion Jones.