US prosecutors said Friday they had dropped their investigation into seven-time Tour de France champion Lance Armstrong and other cyclists without bringing criminal charges.

A statement by US attorney Andre Birotte jnr said Birotte's office "is closing an investigation into allegations of federal criminal conduct by members and associates of a professional bicycle racing team owned in part by Lance Armstrong."

The probe has reportedly included a grand jury sitting in Los Angeles hearing testimony from former Armstrong teammates and associates. Although such grand jury proceedings are supposed to remain secret, the investigation has been widely reported on, prompting Birotte's office to take the step of announcing it had ended.

"The United States Attorney determined that a public announcement concerning the closing of the investigation was warranted by numerous reports about the investigation in media outlets around the world," the statement said.

Armstrong, who won the Tour de France from 1999-2005, has vehemently denied using performance-enhancing drugs during his cycling career. However, he became the subject of the probe by federal investigators who were trying to determine if the US Postal cycling team owed much of their success to a systematic doping program. The investigation was sparked in part by confessed dope cheat Floyd Landis, who claimed Armstrong schooled him in doping techniques when they were teammates. Landis was stripped of his 2006 Tour de France title but didn't admit doping until 2010. 

Last March, US Congressman Jack Kingston criticized the probe, saying he wasn't sure it was an effective use of resources. In July, Armstrong assembled a legal team to combat the leaks of grand jury information in the case, targeting investigators as well as media outlets including The New York Times and The Wall Street Journal. Armstrong said at the time that the leaks were "designed to propagate public support" for the investigation while smearing his reputation. 

Birotte did not give a reason for ending the investigation, and praised the agencies involved. "Mr. Birotte commended the joint investigative efforts of his prosecutors and special agents with the US Food and Drug Administration, the Federal Bureau of Investigation and the United States Postal Service - Office of the Inspector General."