TORONTO -- A Canadian Federal Court judge ruled Thursday that Prime Minister Stephen Harper must press the United States to return a Canadian citizen who is the last Western detainee at Guantánamo Bay.

The man, Omar Khadr, has been held at Guantánamo for more than six years, accused of killing an American soldier when he was 15 in a battle in Afghanistan. He is one of the youngest people ever charged with war crimes.

Harper has steadfastly refused to get involved, saying Khadr faces serious accusations and the legal process in the United States has to play itself out.

Harper maintained that position after the court ruled, telling Parliament on Thursday: ``The facts in our judgement have not changed. We will be looking at the decision very carefully and obviously considering an appeal.''

In his ruling, Judge James O'Reilly accepted arguments from Khadr's lawyers that Harper should seek Khadr's repatriation.

Khadr is now 22, and his lawyers said he was willing to face prosecution in Canada and undergo a transition period away from his family. Some family members reportedly had ties to the terrorist group al Qaeda.

The administration of President Barack Obama is reviewing the Guantánamo cases to determine whether the 220 suspects remaining there should be tried in U.S. courts or released to other countries.

Khadr's lawyers argued that Canada was complicit in the detainee's torture and obliged under international law to demand his return.

In his ruling, O'Reilly said that the Canadian government must intervene.

''The ongoing refusal of Canada to request Mr. Khadr's repatriation to Canada offends a principle of fundamental justice and violates Mr. Khadr's rights,'' O'Reilly said in a written judgment. ``To mitigate the effect of that violation, Canada must present a request to the United States for Mr. Khadr's repatriation to Canada as soon as practicable.''

Dennis Edney, Khadr's lawyer, told The Associated Press that after seven years of fighting, ``the court has truly come to Omar Khadr's rescue.''

Edney said the ruling can only help in getting Khadr returned home.

Edney said the court's order underlines that the government failed to protect a Canadian citizen.

''We have left him languishing,'' Edney said. ``We have not recognized that he is a child. It's a real indictment of the Canadian government.''

Khadr has received some sympathy, but his family has received little in Canada, where they have been called the ``first family of terrorism.''

His father was an alleged al Qaeda militant and financier who was killed by Pakistani forces in 2003, and a brother, Abdullah Khadr, is being held in Canada on a U.S. extradition warrant, accused of supplying weapons to al Qaeda. Another brother has acknowledged that his family had stayed with al Qaeda leader Osama bin Laden.

To allay fears Khadr is a potentially dangerous terrorist, his lawyers propose having him live with either a Muslim or Anglo-Saxon family upon his return to Canada.