Omar Khadr is shown at a U.S. military hearing in Guantanamo Bay, Cuba, in January 2009. (Canadian Press)

The Supreme Court is expected to rule Friday on whether Ottawa has a legal obligation to press for the return of Canadian Omar Khadr from the U.S. military prison at Guantanamo Bay.

The ruling will help clarify the extent to which the courts can wade into federal decision-making about foreign policy matters.

The federal government applied to the Supreme Court in a bid to overturn lower court rulings on the matter.

The Toronto-born Khadr, now 22, was arrested in Afghanistan in July 2002 when he was 15. He is alleged to have thrown a grenade that caused the death of a U.S. soldier. He has been held at Guantanamo Bay, Cuba, since October 2002, awaiting trial on charges of murder, conspiracy and support of terrorism.

On Aug. 14, the Court of Appeal upheld a Federal Court ruling that ordered the government to press for Khadr's return from Guantanamo.

In a 2-1 judgment, the court found that Khadr's rights under Section 7 of the Charter of Rights and Freedoms, which covers the right to life, liberty and security of person, had been breached when Canadian officials interviewed him at the prison in Guantanamo and shared the resulting information with U.S. authorities.

Last April, Federal Court Judge James O'Reilly ruled in favour of Khadr's charter-based challenge of the Canadian government's decision not to request his repatriation from Guantanamo Bay.

The federal government appealed O'Reilly's decision and has long maintained that because of the seriousness of the charges he faces, Khadr should undergo military proceedings in the United States.

The Court of Appeal agreed with O'Reilly that Canada had an obligation to take steps to "protect Khadr from further abuse" and that by refusing to request his repatriation, his charter rights had been violated.

The panel also rejected the Crown's argument that O'Reilly's ruling was a serious intrusion into the conduct of Canada's foreign affairs. It also rejected the government's claim that there is little chance the U.S. will abide by the repatriation request, pointing out that the U.S has, in fact, complied with similar requests from other Western countries.

In his decision, O'Reilly pointed out that Khadr is the last citizen of any Western country held at Guantanamo. Other countries have repatriated their citizens.

Khadr's lawyers argued the Canadian government was complicit in the detainee's alleged torture and mistreatment while in U.S. custody and was obliged under international law to demand his return.