Credit: Jason Kempin/Getty Images for Nike

Lance Armstrong is facing new drug allegations.

In a 60 Minutes interview airing Sunday, former cycling teammate Tyler Hamilton claims that he witnessed the seven-time Tour De France champ using the performance enhancing drug EPO while prepping for the race in 1999, 2000 and 2001.

"I saw it in his refrigerator and I saw him inject it more than one time, like we all did many, many times," said Hamilton of the substance which helps boost endurance.

For his part, Armstrong, 39, took to Twitter to refute the charges. "20+ year career. 500 drug controls worldwide, in and out of competition. Never a failed test. I rest my case," he tweeted Thursday, May 19.

Hamilton's accusations come one year after Floyd Landis admitted to doping and claimed that Armstrong and other teammates also used performance enhancing drugs.

Watch Hamilton's interview, a part of a six-month investigation by 60 Minutes on doping in the cycling circuit, on CBS this Sunday.