Prime Minister Stephen Harper is defending Canada's "rigorous" monitoring of detainees transferred into Afghan custody, despite a top-level internal memo last summer warning his government that Canadians could face legal liability for complicity in torture by working with Afghan secret police.

In this July 2009 file photo, a man Afghan authorities suspect of insurgency-related activities is interrogated during a joint Canadian-Afghan army patrol in the Panjwaii district of Kandahar province. (Colin Perkel/Canadian Press)The memo, shared with CBC News and reported on Tuesday, expresses concern about legal "risks" over Canada's partnership with the Afghan National Directorate of Security (NDS) "without prior insight into its methods" and warns the Afghan intelligence service's wide powers of arrest and detention give it "considerable scope for the use of improper methods."

The report prompted renewed calls from opposition parties for Harper to call a public inquiry into the Afghan detainee affair and suspend ongoing transfers of prisoners into NDS custody.

In an appearance Wednesday in southern Ontario, Harper did not directly address the contents of the memo, but said the Conservative government's 2007 agreement with Afghanistan has ensured prisoners handed over to Afghan authorities are monitored and any allegations of abuse are investigated.

"These reports continue to be things that have been said before, and our position is the same: Whenever there are specific allegations of abuse under the agreement, action is taken to investigate those," Harper told reporters at an event with Ontario Premier Dalton McGuinty in Mississauga.

"There is a rigorous arrangement of monitoring and oversight in the new prisoner agreement, and it has continued to work effectively. As I say, if there are specific problems, they are investigated and appropriate action has been taken. That has been the case for over three years."

Tories misled Canadians: NDP critic

Citing the CBC News report on the document, the NDP said the "only solution" remaining for the government was to stop the transfer of detainees immediately.

"The Conservative government was informed that there would be legal consequences for sending prisoners to the NDS, yet they misled the Canadian people and continued to transfer," NDP foreign affairs critic Paul Dewar said Wednesday in a release.

Harper acknowledged that the 2007 agreement "doesn't mean that things are perfect in Afghanistan."

"No one claims that," he said. "But there are systems in place to monitor, and there is additional capacity [and] building exercises going on with the government of Afghanistan."

Government and military officials, past and present, have vehemently denied allegations by former top diplomat Richard Colvin that Canadian officials continued to transfer detainees into Afghan custody despite knowing about torture allegations.

In his testimony last November before the special parliamentary committee on the Afghanistan mission, Colvin alleged that all prisoners handed over by Canadian soldiers to Afghan authorities were likely subsequently abused and that government officials were well aware of the problem.