Lawyers for Omar Khadr, who is now 21, say they need the documents to make their case at the terror suspect's US military trial in Guantanamo, but the Canadian government refuses to release them in the name of national security.
Canadian intelligence officials interviewed Khadr at the US naval base in the southeastern tip of Cuba in 2003 and passed on information about him to US authorities.
Government attorney Robert Frater said Khadr, the only Canadian held at Guantanamo, had no right to documents detailing those conversations, nor to any other related documents since Canada was not involved in the prosecution.
"Canada is a stranger to the prosecution," Frater told the court.
"In the absence of a Canadian prosecution alleging that he was involved in such actions against Canadian troops, he has no right, no right to any information about what we know about what he may have done," he said.
"Those are national defense or national security matters, and the highest level of protection is accorded to that," Frater said.
Frater said that by asking the high court to consider his case, Khadr's lawyers are "asking a Canadian court to interfere in an American process."
He also warned that foreign governments might hesitate to share sensitive information with Canada in the future if the court rules against the government.
"We don't want to be the disclosure person for the world," he said.
Khadr's Canadian attorney Nathan Whitling, however, said Khadr would not be able to properly defend himself in US legal proceedings if the Canadian government does not convey to his defense team all that they know in the case.
"We're seeking everything that's behind the black curtain," Whitling told the court as Khadr's family watched patiently from the front rows, his young niece toying with her pink dress.
Failing to do so would render the US trial "unfair," he said.
Khadr was detained by the US military in Afghanistan in July 2002. He was among hundreds of people sent to Guantanamo in the wake of the attacks of September 11, 2001.
US authorities accuse him of building explosives and killing a US Army medic during his arrest. His military commission trial is expected to begin this summer.
Human rights groups called for his repatriation, noting that Khadr was a minor when he was detained.
"Omar Khadr is the only child of modern history being accused of war crimes," Roch Tasse, of the International Civil Liberties Monitoring Group, told a news conference.
In the heavily redacted affidavit Khadr tells of brutal treatment after his capture, when he was taken, severely wounded, to a military camp in Bagram, Afghanistan, and later to Guantanamo.
"On some occasions, the interrogators brought barking dogs into the interrogation room while my head was covered with a bag," Khadr said.
He told of rape threats, being shackled to the floor for six hours at a time, being deprived of a toilet and dragged across a floor drenched in urine and pine oil.
"I did not want to expose myself to any more harm, so I always just told interrogators what I thought they wanted to hear," the affidavit quotes Khadr as saying.
He was visited "on numerous occasions" in 2003 by individuals claiming to be from the Canadian government, but the visitors interrogated and threatened him, rather than trying to help him, he said.
Following the last of these visits, he was placed in solitary isolation for a month in a cell kept cold as "a refrigerator," Khadr said.
His legal team accuses Ottawa of "complicity" in the US process and questions the entire legal basis of the Guantanamo trial proceedings.
"Rather than acting to protect the basic human rights of its young citizen, the Crown chose to take advantage of his vulnerability," Whitling said in court documents.
© 2008 Agence France Presse