The treatment of detainees at the hands of their Afghan captors has been a concern "for some time," and Ottawa wants to help that government improve its human rights record, says Defence Minister Peter MacKay.

"The issue around the handling of detainees by Afghans...has been of concern for some time," he told reporters at a news conference in Halifax on Friday.

MacKay said Ottawa routinely compares notes with other NATO countries to see how they transfer detainees to Afghan authorities.

"The reality is this is a responsibility of the Afghan authorities that we want to enhance and support. We've made decisions in the past...to halt the transfer of detainees when credible allegations have come forward."

MacKay said Canada has invested heavily in the Afghan justice system and corrections centres and has worked to put in place "better practices for their handling of detainees."

"That's what we're there to do, to increase their capacity so that they can have a better human rights situation and obviously adhere more with international conventions and improve their standards," MacKay said. "That's very much what we're there to do."

U.S. Defence Secretary Robert Gates, who was present at the same press conference in Halifax, was also asked if the United States had concerns about the treatment of detainees by Afghan authorities.

But Gates deferred to MacKay, saying he did not learn of the issue until he picked up a Canadian newspaper on Friday morning.

MacKay previously said that the testimony of Richard Colvin - the Washington-based intelligence officer and former diplomat who says that likely all detainees handed over to Afghan forces in 2006-2007 were tortured -- was an ill-informed "suspect source" and painted him as a Taliban dupe.

But when asked about the doubt that he had cast on Colvin's allegations on Friday, MacKay said his remarks weren't "personal" in nature.

Colvin testified before the House of Commons special committee on Afghanistan on Wednesday, where he detailed his allegation of the prisoner abuse that he believed was taking place at the hands of Afghan authorities from 2006-2007.

Globe and Mail reporter Graeme Smith told CTV's Canada AM that Colvin was "somebody the Canadian government obviously trusts," who currently holds a sensitive position as Canada's senior intelligence liaison in Washington.

"He's a senior Canadian official and this is probably not the last of it that we've seen, in terms of senior officials throwing accusations back and forth because we're talking about war crimes here. And the blame for all this is percolating upwards in the system and it's going to be a question of who knew what when," said Smith, who has reported extensively on Afghanistan.

Since Colvin's testimony before a House of Commons special committee earlier this week, opposition members have begun campaigning loudly for a public inquiry into the torture issue.

NDP defence critic Jack Harris said an inquiry is necessary because the government's position on Colvin's testimony is "not sustainable."

"I think it's pretty clear that Mr. Colvin's statements, that Mr. Colvin's reports that were made did have credibility, they were based on a variety of things including intelligence reports from other agencies, local human rights agencies," Harris told CTV News Channel during an interview from Ottawa.

In the House of Commons on Friday, Liberal MP Ralph Goodale made a similar argument for having a public inquiry.

"Yesterday, the defence minister was out to shoot the messenger, but the more he called Richard Colvin a liar, the more the minister contradicted himself," Goodale said.

"After four years of denials, he now admits that he did, in fact, receive and read at least one of Richard Colvin's reports. He also admits that at least part of Colvin's story has been corroborated by the Red Cross, the Canadian ambassador and the Canadian Forces."

Goodale then challenged the government to explain why it won't "help Canadians get the whole truth in this matter through a full, independent judicial inquiry?"

In response, Transport Minister John Baird said Colvin did not have any substantial evidence to support the allegations ha made.

"I think it's important to note that in his testimony before the committee earlier this week, Mr. Colvin confirmed that he never witnessed abuse first-hand," Baird said.

He added that much of Colvin's information was second or third-hand, or in the worst case "information that came directly from the Taliban."

"He won't even identify the sources for which he makes these allegations and that's unfortunate," he said.

With files from The Canadian Press