OTTAWA - The Harper government is dismissing calls for a public inquiry into damning allegations that the military handed over prisoners to face torture in Afghanistan.

And it's waging a campaign against the federal intelligence officer who made the charges.

Defence Minister Peter MacKay told a raucous House of Commons on Thursday that there's no evidence to support the allegations by Richard Colvin, even going so far as to describe him as "a suspect source."

Colvin told a Commons committee a day earlier that prisoners were turned over to Afghanistan's notorious intelligence service by the Canadian military in 2006-07 despite warnings that they would be tortured. He also suggested the federal government may have tried to cover up what was happening.

All three opposition parties attacked the Conservatives and demanded an inquiry, but the Tories were unmoved.

MacKay said Colvin had not provided "one scintilla of evidence" that wasn't second-or third-hand information.

He painted Colvin as a Taliban dupe and said Canadians are being asked to accept the word of prisoners "who throw acid in the face of school children, who blow up buses of civilians in their own country."

He side-stepped questions about how a "dupe" could be promoted by Ottawa to serve as an intelligence officer in Washington, where Colvin now serves.

MacKay insisted the government dealt with the concerns over possible torture by revising the prisoner transfer agreement with Afghanistan in May 2007, but conceded later that the agreement was changed partly because of the warnings Colvin issued while in Afghanistan.

Liberal MP Bob Rae described the government's tactics as "reprehensible." He said it's incumbent on the government to answer Colvin's allegations rather than trying to smear him.

New Democrat MP Paul Dewar said the country's reputation as a champion of human rights has been tarnished.

"Torture is never, ever justified," Dewar told a news conference. "Mr Colvin's testimony suggests Canada has failed to meet that moral standard. The damage to Canada's reputation could be serious and lasting."

In his remarks Wednesday, Colvin said he had concerns about the ongoing transfer of prisoners to the Afghan intelligence service.

That prompted the NDP to demand that Canada halt those transfers and negotiate an even better arrangement with the government in Kabul that would put in place even more safeguards to prevent abuse.

Under international law, Ottawa has the responsibility to ensure that prisoners handed over to another nation are not tortured.

Colvin told the special committee on Afghanistan that all of Canada's prisoners captured in 2006 and early 2007 were likely tortured in the hands of the National Directorate of Security, the Afghan intelligence agency.

He said he interviewed four prisoners in the NDS facility in Kabul who showed physical signs of abuse, but could only confirm that one of them was captured by Canadians.

In Kandahar, the general in charge of the military task force said Canada learned its lessons in the handling of prisoners several years ago.

Brig.-Gen. Daniel Menard said the army responded in 2007 after the allegations of abuse first surfaced.

He said there are more rigorous handover procedures and new safeguards to ensure prisoners could be monitored more effectively once in Afghan custody.

"One thing that has been done right from the beginning is that every time that we have heard about anything to do with torture or something that was similar to this, some actions were taken by this task force in order to correct this," he said.

Also Thursday, a Red Cross official in Washington clarified remarks that came out of the Commons committee the day before.

Spokesman Bernard Barrett said the agency tried and failed to get in touch with Canadians in Kandahar three times in 2006 - not to warn them about Afghan prison conditions, but rather the routine matter of discussing the country's responsibilities in notifying the Red Cross.