Omar Khadr has fired his American lawyers less than a week before his military commission pre-trial hearings are slated to resume in Guantanamo Bay, one of his attorneys said Wednesday.

In this courtroom sketch from June, Omar Khadr sits with his defence team during a hearing at Guantanamo Bay in Cuba. (Janet Hamlin/Reuters)

Khadr, via a motion terminating his U.S. counsel and filed by his lawyers with the commission, said that he would either represent himself or boycott his trial.

"We have worked our hearts out on the case and were just eagerly looking forward to what we had planned to do," one of the lawyers, Barry Coburn, told The Canadian Press.

"We're just kind of consumed with grief at the notion that we won't be able to do that."

Coburn, who said he was "totally devastated" by Khadr's decision, refused to say what may have motivated his Canadian client, citing solicitor-client privilege.

However, speaking from Baltimore after a flight from Guantanamo Bay, Coburn said he hoped Khadr would relent.

"As of right now, there is no indication of that."

Army Col. Patrick Parrish, the military judge presiding over Khadr's case, will have to rule on the motion axing the lawyers after a hearing on Monday.

The Toronto-born Khadr, 23, is accused of five charges, the most serious of them being the murder of an American special forces soldier.

Prosecutors allege Khadr threw a hand grenade that killed Sgt. Chris Speer in Afghanistan in July 2002 when he was 15 years old. He faces a maximum life sentence on conviction.

His trial is slated to start in August. It was not immediately clear what impact the firing of the lawyers would have on the timing.

Khadr is also represented in the United States by Kobie Flowers and Pentagon-appointed lawyer Jon Jackson.

Flowers refused comment, citing his "ongoing duty of loyalty" to his client.

However, one of Khadr's Canadian lawyers, Nate Whitling, said from Edmonton that Khadr had "simply lost hope" in any prospect of a fair trial in Guantanamo.

"He sees little point in participating in a prosecution which appears will be conducted on the basis of statements extracted from him while he was being threatened, abused and tortured," Whitling said.

Pre-trial hearings were to resume next week, after a recess to allow the prosecution to conduct its own assessment of Khadr's mental state.

His lawyers have previously pressed to have self-incriminating statements and other evidence thrown out on the basis it was obtained through torture after the badly wounded Khadr was captured.

Khadr was taken to Guantanamo Bay in October 2002 and is the lone Westerner and youngest inmate at the U.S. prison.