WASHINGTON - Canadian terrorism suspect Omar Khadr lost his last bid Monday to have the U.S. Supreme Court review his murder case before he faces trial at Guantanamo Bay.

The top court issued a one-line decision refusing to hear arguments on Khadr and another detainee, Salim Ahmed Hamdan, a Yemeni.

The move wasn't surprising given the American court's refusal in early April to hear related arguments from other Guantanamo prisoners.

But the result, said U.S. civilian lawyer Muneer Ahmad, is unfortunate for everyone.

"Without the scrutiny of the courts, the military commissions will continue to operate under a cloud of illegitimacy,'' said Ahmad, who argued the new tribunal system approved last year by Congress is no better and still allows evidence obtained through torture.

"As the secretary of defence recently stated, the rest of the world believes the commissions are tainted. The court's action does nothing to dispel that view.''

Khadr, 20, has been designated an enemy combatant and held by U.S. authorities since he was 15 years old. He's accused of throwing a grenade in a July 2002 firefight in Afghanistan that killed Sgt. 1st Class Chris Speer, an elite Delta Force officer.

The Canadian attended some pre-trial hearings in January 2006 before the American court, responding to a challenge from Hamdan, declared the system illegal and forced President George W. Bush to seek congressional approval for changes.

Khadr, who faces life in prison, has been refusing to meet with his lawyers and has threatened to boycott his trial. He was officially charged again last week with murder, attempted murder, conspiracy, spying and providing material support for terrorism.

In addition to American attorneys, Canadian lawyers Dennis Edney and Nate Whitling will likely act as so-called foreign attorney consultants.

The U.S. Supreme Court's decision to stay out of the tribunals for now means Khadr, if convicted, would face a long appeal process.

"They've set up this system that the Supreme Court was less likely to pre-empt,'' said Shayana Kadidal, senior managing attorney of the Guantanamo project at the Center for Constitutional Rights in New York.

"And some of the charges were made up after the fact to ensure they could get a conviction.''

Khadr was born in Toronto, the son of an al Qaeda financier killed in Afghanistan in 2003. The family's ties to terror leader Osama bin Laden have outraged some Canadians who say Khadr's mother and siblings should be stripped of their citizenship.

His lawyers have urged Canadian officials to ensure the he could serve any prison time at home like Australian David Hicks, who reached a plea deal with U.S. authorities last month.

But they say they they have no sense Canada, which has been mum on the U.S. prison camp in Cuba condemned by most western countries, is willing to negotiate a political solution.

In early April, the U.S. Supreme Court directed prisoners challenging their detention to the federal Court of Appeals, which can only decide whether the military followed proper procedures in defining them as unlawful enemy combatants instead of prisoners of war covered by the Geneva Conventions and eligible for regular military courts martial.

The Justice Department recently filed court papers to severely restrict the access of defence lawyers to their Guantanamo clients.

Lt.-Col. Colby Vokey, Khadr's chief military lawyer, called the move "disturbing and offensive.''

"I don't know how this might affect my visitation with Omar. Access to my client has already been problematic and restrictive enough.''