Amnesty International Canada has joined opposition MPs in calling for a public inquiry into the alleged torture of detainees turned over to Afghan authorities by Canadian troops.

"It is very clear that existing possibilities which might get to the bottom of other issues of national concern, such as questions in the House of Commons, hearings before parliamentary committees, or proceedings before courts or tribunals, are not going to shed the light that is needed here," said Alex Neve, secretary general of Amnesty International Canada. "The obstruction has run too deep."

Opposition MPs have also called for an inquiry following the testimony of Richard Colvin, a former Canadian diplomat in Afghanistan who told a House of Commons committee last week that all of the prisoners Canada handed over in 2006-07 were likely tortured.

Colvin testified that his concerns were ignored by top government officials and the government may have tried to cover up the issue.

The Tories have rejected calls for an inquiry and have raised questions about the credibility of Colvin's testimony.

"Rather than ensure that light will be shed on serious human rights concerns of international significance, the government has insisted instead to obstruct, hide, and deny these concerns," Neve said.

Neve said his organization has written to Prime Minister Stephen Harper, demanding an inquiry be held into the issue.

In 2007, Amnesty and the British Columbia Civil Liberties Association filed a case in federal court, demanding the transfers of detainees be stopped.