The Supreme Court of Canada will not hear the extradition case of Abdullah Khadr, shutting the door on American efforts to prosecute the man in a terrorism case.

The high court has dismissed the federal government's leave-to-appeal application in the case of Khadr, the older brother of Omar Khadr, the last Western detainee to be held at Guantanamo Bay.

The federal government, acting on behalf of the Americans, was appealing rulings by lower courts that prevented Abdullah Khadr from being extradited to the United States.

Ottawa had argued it was wrong to prevent an "admitted" terrorist from facing trial in the U.S.

Last year, the Ontario Superior Court decided there were sufficient grounds to send Khadr to the U.S. based on self-incriminating statements he'd given the RCMP.

However, the court ruled the U.S. had violated fundamental justice with its involvement in Khadr's "shocking" mistreatment during 14-months' detention in Pakistan, a decision that was upheld by the Ontario Court of Appeal.

As is the usual practice, the Supreme Court gave no reasons for why it dismissed the leave to appeal application.

The federal government had argued that Canada's ability to comply with its international obligations could be compromised if the decision staying the extradition of Khadr was allowed to stand.

"This case raises issues of national importance that require consideration by this court," the federal Justice Department said in its leave-to-appeal request, a copy of which was obtained by The Canadian Press.

Principles of fundamental justice "should not be used to impose the technicalities of our criminal law on a foreign partner," the request argued.

Khadr's lawyer Dennis Edney had characterized the federal government's appeal of the case as being "entirely devoid of merit."

Edney said beforehand the government's now-rejected appeal "fails to identify even an arguable ground of appeal, much less a legal issue of public importance."

He called the government's attempt a waste of public resources.

Younger brother remains in Guantanamo

Thursday's decision is the latest twist in the long legal saga involving a Canadian family with close ties to al-Qaeda.

Khadr is the oldest son of the late Ahmad Said Khadr, an associate of Osama bin Laden.

His brother, Omar, pleaded guilty a year ago to war-crimes charges that included murder for throwing a grenade that mortally wounded a U.S. soldier in Afghanistan.

As part of a pretrial agreement for his guilty plea, the younger Khadr, now 24, was to be released from the U.S. military prison at Guantanamo Bay, Cuba, and was eligible to return to Canada by Nov. 1 to continue serving his sentence.

So far, Khadr remains in Guantanamo.

In October 2004, the U.S. paid Pakistani intelligence agents $500,000 to kidnap Abdullah Khadr.

He was prevented from speaking to consular officials and beaten until he co-operated with Pakistani intelligence.

American agents also interrogated him in Pakistani detention and got him to admit he had procured weapons for al-Qaeda.

The Pakistanis freed Khadr without charge and he returned to Canada in December 2005. He was arrested by Canadian authorities at the request of the U.S. so he could be extradited.

In August 2010, Ontario Superior Court Justice Christopher Speyer ruled there were sufficient grounds to send Khadr to the U.S. based on self-incriminating statements he'd given the RCMP.

However, Speyer stayed the extradition, on the grounds the U.S. had violated fundamental justice with its involvement in Khadr's "shocking" mistreatment during his time in custody in Pakistan.

Extraditing him would only serve to reward the Americans' "gross misconduct," Speyer ruled.

This past May, the Ontario Court of Appeal upheld Speyer's ruling.