Canada's federal government is urging the country's top court to overturn a judicial order that obligates the government to seek the repatriation of the youngest detainee held by the U.S. at Guantanamo Bay.

Conservative Prime Minister Stephen Harper has steadfastly refused to request the return of Omar Khadr, the last Western detainee held at the prison at the U.S. Navy base in Cuba. Harper has said the U.S. legal process must be allowed to play itself out.

Khadr, who was born in Toronto, is now 23 years old but was only 15 when he was captured after allegedly killing an American soldier with a grenade during a 2002 battle in Afghanistan. Authorities say his family has close links to Al Qaeda.

A government lawyer argued before the Supreme Court Friday that courts do not have the right to order authorities to seek Khadr's repatriation.

"We're in the realm of diplomacy here," federal lawyer Robert Frater told the court. "The government has the right to decide what requests should be made, how they should be made, and when they should be made. The courts are not in the best position to do that."

Khadr's lawyers contend that Canada was complicit in his alleged torture and maintain that Harper is obliged under international law to demand the prisoner's return so as to protect children and child soldiers and to repudiate torture. The U.S. has assured Canadian authorities that Khadr has been treated humanely. Canadian officials questioned Khadr at Guantanamo and shared the results of their interrogations with U.S. authorities

Supreme Court Chief Justice Beverley McLachlin acknowledged that Khadr "suffered greatly" but asked one of Khadr's defense lawyers how demanding or ordering repatriation would fix something that happened in the past.

The Supreme Court reserved its decision for a later date.

The Canadian hearing was held on the same day that the U.S. Justice Department announced that Khadr would be among five Guantanamo detainees whose cases would be heard by military commissions in the U.S. on a variety of terrorism charges.

It was not immediately clear where Khadr and the other detainees would be sent, but a military jail at a Navy base in South Carolina has been high on the list of sites under consideration.

U.S. Attorney General Eric Holder emphasized that Khadr is headed for trial by a military commission but he didn't rule out possibly reviewing the detainee's disposition "as that case proceeds."

Conservative lawmaker Pierre Poilievre, parliamentary secretary to the prime minister, welcomed the U.S. decision to send Khadr to a U.S. military commission.

"We acknowledge the decision of the Obama administration to prosecute Omar Khadr through the U.S. military commission system and we believe the U.S. military process announced today should run its course," he said.

Dennis Edney, Khadr's Canadian lawyer, called the U.S. decision to send Khadr to a military commission a tragedy.

"It's quite an indictment on what Obama stands for when he talks about human rights," Khadr said. "Omar will be still stuck in the same military commission apart from a few cosmetic adjustments. Torture memos will still be permitted. It's a tragedy for the system of justice and it's a tragedy for Omar Khadr."

Edney said he thinks the U.S. would like to send Khadr home if Canada requested it, but he offered no evidence to back up his suggestion.

In April, a Canadian judge ruled that Harper's refusal to request Khadr's repatriation offends a fundamental sense of justice and violates his constitutional rights.

Canada's Court of Appeal dismissed the government's appeal of that decision this past summer by a majority 2-1 decision.

Khadr, the son of an Egyptian-born father and Palestinian-born mother, has said through his lawyer that he would be willing to face prosecution in Canada and undergo a transition period away from his relatives, who have Canadian citizenship but have been linked to Al Qaeda.

Canada's three opposition parties have demanded that the Conservative government bring Khadr home.

Khadr has received some sympathy from Canadians, largely due to his age and the torture allegations, but his family has been widely criticized and called the "first family of terrorism."