By Lee Carter
BBC News, Toronto
Canadian opposition parties are calling for the country's defence minister to resign following allegations that detainees were tortured in Afghanistan.
Canada has 2,500 soldiers serving in Afghanistan
The torture is said to have occurred after Canadian soldiers transferred suspects to Afghan security forces.
About 2,500 Canadian soldiers are involved in combat operations against insurgents in southern Afghanistan.
Canada signed a controversial agreement two years ago to hand over Taleban prisoners to the Afghan authorities.
At least 30 detainees told Canada's Globe and Mail newspaper that they were tortured in Afghan prisons after being handed over by Canadian armed forces based in Kandahar to Afghanistan's National Directorate of Security.
The allegations of brutality range from beatings to starvation, to being left naked outside in freezing temperatures.
Some of the men also say they were whipped with electrical cables.
In the face of a storm of opposition questions in the Canadian parliament, Prime Minister Stephen Harper defiantly defended the controversial prisoner exchange deal.
He said the allegations would be investigated by Afghanistan's Independent Human Rights Commission, which agreed in February to monitor the fate of detainees.
Canadian Defence Minister Gordon O'Connor also promised that the allegations would be looked at seriously.
But two professors who specialise in international law and human rights held a news conference in Ottawa to warn the government that if the allegations are true, then Canadians may face international war crimes prosecution.
One of the professors, Amir Attaran, introduced research in February which raised the possibility that some detainees may also have been abused while in Canadian custody.