The U.S. Supreme Court has refused to hear the case of Omar Khadr, the only Canadian imprisoned at the U.S. detention centre in Guantanamo Bay, Cuba.

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Omar Khadr, seen in this 2002 photo, has been in U.S. custody since he was captured in Afghanistan at the age of 15. ((File photo))

The top American court has also refused to hear the case of another Guantanamo prisoner, Salim Ahmed Hamdan of Yemen, the court announced Monday.

Both prisoners were challenging the legality of the military commissions that are scheduled to hear their cases.

Khadr, a 20-year-old whose family lives in the Toronto area,is scheduled to have his caseheard by a military commissionwithin four months.

Khadr is accused of throwing a grenade that killed a U.S. medic in Afghanistan in 2002. He also faces charges of attempted murder, conspiracy, spying and providing material support for terrorism.

He has been in U.S. custody since he was seized in Afghanistan at the age of 15.

Other members of his immediate family have also beenaccused of having ties to terrorist activities.

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Guantanamo prisoner Salim Ahmed Hamdan was at the heart of a 2006 U.S. Supreme Court ruling. (Neal Katyal/Associated Press)

Hamdan, charged with conspiring to harm U.S. citizens, has admitted to being a driver for al-Qaeda leader Osama bin Laden but denied taking part in the Sept. 11, 2001, attacks against the United States.

He was at the heart of a 2006 case in which the Supreme Court declared U.S. President George W. Bush's system of military commissions illegal and in violation of American and international law.

As a result of that ruling, the Bush administration made changes to its military commissions, which now have congressional approval.

But lawyers for Khadr and Hamdan argue that the new system is almost identical to the old one, with coerced testimony still allowed.

The lawyers had hoped to challenge the new system before the Supreme Court.

With files from the Associated Press