Prosecutors handling an investigation of doping allegations against champion cyclist Lance Armstrong have responded to complaints about leaks in the grand jury inquiry without publicly revealing their response.

The U.S. Attorney's Office spokesman Thom Mrozek said Monday that it had filed its reply under seal to avoid violating rules that protect the secrecy of grand jury proceedings.

Armstrong's attorneys filed a motion in July, claiming leaks in the grand jury inquiry have sullied the reputation of the seven-time Tour de France winner. The initial filing, which was left unsealed, claimed some of the material reported by The Associated Press, Wall Street Journal, New York Times and others could have only come from government officials forbidden under law from discussing the proceedings.

A judge had asked U.S. prosecutors to respond to the motion by Monday.

Armstrong's lawyers are seeking a judge's order requiring federal agents to detail their conversations with reporters and to hold federal officials in contempt for the leaks. The lawyers have also suggested that, in a last resort, the court could force journalists to reveal their sources.

For more than a year, a grand jury in Los Angeles has been investigating claims that Armstrong used performance-enhancing drugs during his run of Tour de France victories, but no charges have been filed.

Prosecutors have not publicly detailed their case against the cyclist and advocate for cancer patients, but several of his teammates and associates have been called before the grand jury.

The cyclist's attorneys cited more than two dozen articles between May 2010 and June 2011 about the investigation. Armstrong has denied he ever doped.

Lawyers for Armstrong, who is a cancer survivor and whose Livestrong Foundation has raised millions for cancer research, claim news about the case has damaged his public image.

"Each leak has been designed to propagate public support for this investigation by smearing Armstrong and tarnishing his reputation," their initial filing stated. "The tactical nature of these leaks cannot be ignored as it strongly suggests an underlying partisanship inherent in government agents."