Canadian Prime Minister Stephen Harper brushed off evidence that US interrogators had abused a Canadian terrorism suspect in Guantanamo Bay, saying the man's trial should go ahead anyway.

An official document released in Ottawa on Wednesday showed US authorities told a Canadian investigator in 2004 that they had deprived Omar Khadr of uninterrupted sleep.

Khadr, 21, is the only Western prisoner still held at the prison at the US naval base at Guantanamo Bay, Cuba.

He faces charges of throwing a grenade that killed an American medic and wounded another soldier during a fight at an al Qaeda compound in Afghanistan in 2002 when he was 15.

Harper -- who regularly criticizes other nations for abusing human rights -- has ignored pleas to intervene in Khadr's case, saying the man faces serious charges.

Critics of Khadr's treatment say he is a child soldier who should be rehabilitated rather than punished.

Harper, in Japan on an official visit, did not respond directly when reporters pressed him about the document.

"We always act as a government on the basis of our legal advice and our legal obligations. The previous government took all of the information into account when they made their decision on how to proceed with the Khadr case," he said.

Asked again to respond to the details of how Khadr had been treated, Harper replied: "Frankly, there is not a real alternative to this legal process now to probe the truth concerning these accusations (of killing the medic). We think this legal process should go ahead."

At the time of Khadr's arrest, the Liberals were in power in Canada. They were replaced by Harper's Conservatives after a January 2006 election.

The official document showed Khadr, then a teenager, had been put into a "frequent-flyer program" in which he was moved every three hours to make him more amenable to talking.

A Canadian judge last month ordered the release of the document, saying the measures taken by US authorities violated international human rights law.

Ottawa tried to deny Khadr's attorneys access to the document on the grounds the information was given to Canada in confidence and its disclosure would hurt US-Canada ties.

Khadr alleges US interrogators repeatedly threatened to rape him or send him to another country to be raped.

Harper said Canada had repeatedly sought and received reassurances that Khadr was being treated fairly.