OTTAWA - Canada's spy agency has ordered a "comprehensive review" of its dealings with detainees in Afghanistan amid questions about its role in conducting interrogations.

The Canadian Security Intelligence Service quietly informed Public Safety Minister Vic Toews the review is designed to ensure the agency can clearly account for its involvement with Afghan prisoners, an internal memo obtained by The Canadian Press reveals.

The study could shed fresh light on the spy agency's interrogation of prisoners in the early years of the war in Afghanistan -- one of several efforts to determine whether Canadian authorities knowingly transferred detainees into the hands of torturers.

"Given the high media profile and controversial nature of this issue, the Service has begun a comprehensive review of all its activities related to Afghanistan detainees," says the March memo to Toews, which was copied to the national security adviser to Prime Minister Stephen Harper.

"This review is being conducted to ensure that the Service can clearly and without reservation account for its engagement during this period."

A heavily censored copy of the memo, originally classified secret, was released under the Access to Information Act.

It shows the spy service scrambled to brief Toews after The Canadian Press requested comment for a forthcoming story that revealed CSIS had worked alongside the military to question captured Taliban fighters.

Information from sources and witness transcripts filed with the Military Police Complaints Commission, which was probing the role of police in the transfers, indicated CSIS was called in to assist soldiers inexperienced at eliciting useful information.

The spies would sometimes make recommendations on which prisoners to hand over to the National Directorate of Security, Afghanistan's notorious intelligence service, sources said, though Canadian military officials always had final say.

CSIS questioned Afghan detainees from 2002 through late 2007, when the military began to conduct interrogations without assistance, Michel Coulombe, the service's assistant director for foreign collection, told the Commons special committee on Afghanistan in May. The timeline roughly coincides with Canada's direct contribution to Operation Enduring Freedom, the U.S.-led war on terror.

Later in May, CSIS director Dick Fadden elaborated briefly on the agency's role, telling the Commons public safety committee the service was "frequently brought in" to ask captives questions, "usually to try to ascertain their identity, to try to find out what they had been up to. In most cases, these interviews lasted less than 15 or 20 minutes."

But he also hinted that the spy service continues to play a supporting role, within its broad mandate to protect Canadian interests.

"Basically, what we do is try to talk to people in Afghanistan who would have some intelligence, some information, about threats to both Canada and to our allies," he told MPs. "By definition, those people are either terrorists themselves, Taliban insurgents, or they're people who know something about them. So our job is, in one shape, form, or another, to try to acquire that kind of intelligence."

How the agency conducts its Afghan operations has never been discussed publicly.

It's been suggested CSIS officers at one time worked alongside the American CIA and in close co-operation with Canada's secretive, elite JTF-2 commandos from a secluded base in Kandahar known as Graceland.

Neither CSIS nor Public Safety would discuss the internal review.

"Any information from the director to the Minister is provided in confidence. We will therefore not comment on the particular issue," said CSIS spokeswoman Isabelle Scott.

Public Safety said it does not comment on "operational security matters related to CSIS."

The March memo says CSIS's "role and involvement with Afghan detainees has been limited."

It stresses the spy agency's contact with detainees came only at the request of the Canadian Forces.

"The Service has no indication that the detainees with which we were involved were abused or mistreated by either Canadian or Afghan authorities."

Wesley Wark, an intelligence specialist at the University of Toronto's Munk School of Global Affairs, said he's a bit startled CSIS would order such a review to prove after the fact its role was benign.

The agency may be engaged in a "damage control exercise" or it is looking to learn something from its involvement in prisoner interrogation, he said.

"My gut feeling is that this was an unplanned mission and they went at it in the heat of the moment," Wark said in an interview. "They may have a feeling this was done in a hurry and they'd better know precisely what went on when people start asking them."

The Security Intelligence Review Committee, a watchdog over CSIS that reports to Parliament, is also preparing a study of the agency's involvement with Afghan detainees.

An all-party group of parliamentarians, meanwhile, has received clearance to review highly classified government documents on the affair. A panel of jurists will decide on publication of these records after considering the security implications.

It is widely believed that a high-profile dispute over MPs' access to the records prompted the government to prematurely end the parliamentary session earlier this year.

The Military Police Complaints Commission initially asked questions about CSIS's role in Afghanistan, but dropped the line of inquiry when it became entangled in legal challenges about its authority to investigate Ottawa's overall prisoner-transfer policy.

The lawyer for the two human rights groups, whose complaints launched the controversy over Afghan prisoners, was equally mystified at why the internal review was ordered.

Paul Champ said the spy agency's operations in Afghanistan have been cloaked in secrecy and any investigation would help explain things.

"What exactly they are doing, what is their mandate, what kind of accountability mechanisms are in place, these are all questions that haven't been answered," Champ said in an interview. "We don't know anything."