The agency plans to share everything it knows with the Americans, a French official told The Associated Press.
U.S. Food and Drug Administration Agent Jeff Novitzky, federal prosecutor Doug Miller and U.S. Anti-Doping Agency CEO Travis Tygart are in France for the probe, the AP reported. The former head of the French agency, Pierre Bordry, previously pledged to hand over Armstrong's samples from the 1999 Tour de France to Novitzky. French sports daily L'Equipe reported in 2005 that Armstrong's samples from 1999 contained traces of the banned performance-enhancer EPO.
Mark Fabiani, counsel for Armstrong, denied that any of his samples ever tested dirty and said the cyclist does not fear the investigation.
"The samples were clean when originally provided and tested," Fabiani told NBC. "So we have nothing to be concerned about. Period."
Indeed, an investigator mandated by cycling's international governing body, the UCI, later cleared Armstrong and the seven-time Tour de France winner has steadfastly denied cheating.
Allegations against Armstrong were renewed this spring after disgraced Tour de France winner Floyd Landis, who was stripped of the 2006 title after failing a doping test, accused Armstrong and others of systematic drug use.
In related news, The New York Times reported that police in Italy raided the house of Yaroslav Popovych, a RadioShack teammate of Lance Armstrong, as part of a doping investigation there.