Los Angeles - US prosecutors said on 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 jr 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 team-mates 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.
"This is great news," Armstrong lawyer Mark Fabiani said in a statement. "Lance is pleased that the United States Attorney made the right decision, and he is more determined than ever to devote his time and energy to Livestrong and to the causes that have defined his career."
The US Anti-Doping Agency, however, said it continued to investigate allegations of doping in cycling and hoped to have access to the information gathered in the criminal probe.
"Unlike the US Attorney, USADA’s job is to protect clean sport rather than enforce specific criminal laws," USADA chief executive Travis Tygart said.
"Our investigation into doping in the sport of cycling is continuing and we look forward to obtaining the information developed during the federal investigation."
Armstrong, who won the Tour de France from 1999-2005 and used his fame to fuel his charitable work for cancer awareness, 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 team instituted a systematic doping programme - particularly while it received government sponsorship through the US Postal Service.
The federal probe apparently began with an investigation into a small US racing team, Rock Racing, and broadened after confessed dope cheat Floyd Landis claimed Armstrong schooled him in doping techniques when they were team-mates.
Landis was stripped of his 2006 Tour de France title but didn't admit doping until 2010.
Last March, US Congressman Jack Kingston criticised 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."