A Canadian judge has ruled that PM Stephen Harper must immediately press the US to send home a Canadian detainee being held at Guantanamo Bay.
The judge upheld the view of lawyers for Omar Khadr that the government's refusal to ask for his repatriation infringed his constitutional rights.
Mr Khadr has been held for six years, accused of killing a US soldier in Afghanistan when he was 15.
Mr Harper has argued that the US legal process should be allowed to continue.
He told parliament after the court ruling on Thursday: "The facts in our judgement have not changed.
"We will be looking at the decision very carefully and obviously considering an appeal."
Mr Khadr's lawyers said he was willing to be tried in Canada.
He is now the only detainee from a Western nation being held in the US military camp.
His case was among the first to be suspended following an order from Barack Obama, in one of his first acts as US president, to temporarily halt to all tribunals pending a review of the process.
Judge James O'Reilly said in his written ruling: "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.
"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."
One of Mr Khadr's lawyers, Dennis Edney, said "the court has truly come to Omar Khadr's rescue," Associated Press reported.
His mother, Maha Khadr, told AP: "Everything is contradictory.
"Canada is one of the countries that supports the rights of child soldiers and Canada is the last to support Omar, the last."