United States federal prosecutors say they are closing a criminal investigation of Lance Armstrong, the seven-times Tour de France winner, and will not charge him over allegations that he used performance-enhancing drugs.

The US attorney Andre Birotte Jr said the case had been closed but did not give the reason. Investigators looked at whether a doping programme was created to keep Armstrong and his team-mates running at the head of the pack while, at least part of the time, they received government sponsorship from the US Postal Service.

Armstrong's attorney Mark Fabiani welcomed the decision in a statement. "This is great news," he said. "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."

However the US Anti Doping Agency CEO Travis T Tygart has said that the matter is not over. "Unlike the US Attorney, Usada's job is to protect clean sport rather than enforce specific criminal laws," he indicated in a statement. "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 won the Tour de France every year from 1999-2005 and has always fiercely denied doping.

The investigation, anchored in Los Angeles where a grand jury was presented evidence by federal prosecutors and heard testimony from Armstrong's former teammates and associates, began with a separate investigation of Rock Racing, a cycling team owned by the fashion entrepreneur Michael Ball.

Birotte Jr announced that his 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 Armstrong probe was led by the federal agent Jeff Novitzky. US authorities sought assistance overseas, requesting urine samples of US Postal riders from France's anti-doping agency and also meeting officials from Belgium, Spain and Italy.

Prosecutors also subpoenaed Armstrong supporters and former team-mates to testify in Los Angeles. Among them were the Ukrainian cyclist Yaroslav Popovych, who rode on three Armstrong teams dating back to 2005; Allen Lim, an exercise physiologist for Team Radioshack; and the long-time Armstrong friend Stephanie McIlvain.

The investigation was spurred by the disgraced cyclist Floyd Landis, who claims Armstrong had a long-running doping system in place while they were team-mates. Landis, who was stripped of the 2006 Tour de France title for drug use, acknowledged in 2010 he used performance-enhancing drugs after years of denying he cheated.

One of the most serious accusations came during a "60 Minutes" interview last May when another former team-mate, Tyler Hamilton, said he saw Armstrong use EPO during the 1999 Tour de France and in preparation for the 2000 and 2001 tours.

As the investigation progressed, Armstrong assembled a legal team, hired a spokesman and briefly created a website to address any of the allegations reported.