Opposition members are pushing for a public inquiry into the Afghan torture issue, while the Conservative government seeks to undermine the diplomat who repeatedly warned Ottawa about the problem.

In a set of explosive allegations made public earlier this week, Richard Colvin told a House of Commons special committee that all detainees captured by Canadian Forces in Afghanistan were tortured after being handed over the Afghan authorities.

In response, Defence Minister Peter MacKay has described Colvin as a "suspect source" who has been duped by Taliban-planted stories in Afghanistan.

In the House of Commons on Thursday, MacKay said the ex-diplomat hadn't provided "one scintilla of evidence" that wasn't second or third-hand information.

But the defence minister side-stepped questions about how a "dupe" could be promoted to work as an intelligence officer in Washington, where Colvin works today.

Colvin learned of the problem in 2006, when he was Canada's No. 2 diplomat in Afghanistan. From 2006-2007, he wrote reports that were widely circulated among the foreign affairs and defence departments that warned of torture in Afghan jails.

But senior members of the government said they did not see these reports early on and MacKay has questioned why Colvin didn't come directly to them with the allegations he has recently made public.

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.

Following Colvin's testimony earlier this week, opposition members quickly began asking for a public inquiry, and challenging the government on the torture issue, which spurred the remarks by MacKay on Thursday.

Liberal MP Bob Rae said the government's tactics were "reprehensible," and said the government is obliged to respond to the allegations Colvin has raised and not smear him.

NDP Jack Layton said that it's only "a matter of time" before an inquiry is called and that it's unacceptable for the government to attack a whistleblower who went by the book.

Globe and Mail reporter Jane Taber told Canada AM that MacKay's remarks in the House of Commons suggested the government's approach is to attack Colvin's credibility and to criticize those who believe him.

"What (MacKay) did, and what it seems the government officials are doing, is basically attacking the credibility of (Colvin's) evidence and also attacking his credibility in an interesting way, by suggesting that anyone who listens to what he has to say is...a Taliban supporter," Taber said during a phone interview from Ottawa on Friday morning.

Prime Minister Stephen Harper, who has just returned to Canada after travelling to India, has yet to comment on the allegations raised this week.

With files from The Canadian Press