A day after a former diplomat made explosive allegations that Ottawa was aware of routine torture practices in Afghanistan, the Conservatives attacked his credibility, saying there was "no evidence" to support the claims.

Defence Minister Peter MacKay defended the government from Richard Colvin's allegations, who testified under oath that torture by Afghan intelligence forces was endemic over a two-year period.

The Tories have rejected calls for a public inquiry into the allegations.

"This is a witch hunt," MacKay said, replying in Parliament to accusations from Liberal defence critic Ujjal Dosanjh.

However, MacKay was forced to concede that Colvin's reports on torture helped convince the government to work out a new prisoner transfer agreement two years ago.

Colvin has also been trusted with a top level intelligence job at the Canadian embassy in Washington and MacKay said he could not answer why the official was given a top job even though the government was attacking his credibility.

During an interview on CTV's Power Play on Thursday, MacKay said that Colvin's accusations were based on information which may have been propagated by Taliban sources.

"Serious allegations require serious investigation," MacKay said.

However, when pressed on the fact that Ottawa did in fact alter the practice of transferring prisoners after Colvin's concerns were made public, MacKay said that "other sources helped substantiate that evidence."

However, The Canadian Press reported that top officials from Ottawa discussed the possibility that Kandahar's then-governor was involved in torture in 2006. The concerns were later dismissed.

One source told CP that the gathering took place at the Privy Council Office and was attended by Harper's security adviser at the time, Margaret Bloodworth.

MacKay slammed Colvin for not raising his concerns on the torture issue in person while in Afghanistan.

Colvin said he voiced his concerns through the proper channels and when cabinet ministers visited Afghanistan, his job was to make sure their trip went smoothly.

"It would be inappropriate, I think, to come and ruin their visits by saying 'Hey, you know detainees are being tortured with electricity,'" he said.

The allegations

Dosanjh claimed that the Conservatives were either hiding the truth or completely intentionally ignorant.

"It is unthinkable that the prime minister and the ministers did not know," said Liberal defence critic Ujjal Dosanjh. "Willful blindness Mr. Speaker, is cover-up too."

MacKay denied the accusation, saying: "We inherited a situation that was very difficult with respect to the handling of Taliban prisoners. What we did was act upon advice from a number of diplomats, including the ambassador."

He added that the government has invested in the Afghan justice system and worked to provide proper training in the handling of prisoners.

"To suggest that every single Taliban prisoner was tortured is not credible," MacKay said.

Colvin, now a Washington-based senior intelligence officer, told a House of Commons committee Wednesday that from 2006 to 2007, it was standard practice for Afghan authorities to torture their detainees.

Back then, Colvin served in the No. 2 diplomatic post in Afghanistan for an 18-month period. He said he repeatedly told Ottawa in writing about torture allegations, but he was ignored. He claimed that he was asked to stop putting his accusations in writing.

MacKay dismissed this as "ridiculous," and "completely unsubstantiated."

During question period, MacKay alleged Colvin did not have first-hand evidence of any abuse against prisoners that were transferred, and could not confirm if marks observed on prisoners stemmed from abuse.

"There (are) incredible holes in the story that have to be examined," MacKay said.

"There is not one bit of evidence, not a scintilla, that points to mistreatment of Taliban prisoners by the Canadian Forces."

He said that the government changed the system in Afghanistan more than two years ago.

"When we've had specific allegations of abuse, we've acted, and we will not tolerate proven evidence of abuse," said Foreign Affairs Minister Lawrence Cannon, who was in Kabul for the inauguration of Afghan President Hamid Karzai.

According to what Colvin told the special committee on Afghanistan, prisoners were beaten and subjected to electric shocks. And in some cases, the roundup of detainees resulted in innocent people being tortured, which Colvin says has eroded Canada's standing among Afghans.

"In my judgment, some of our actions in Kandahar, including complicity in torture, turned local people against us," Colvin said.

"Instead of winning hearts and minds, we caused Kandaharis to fear the foreigners."

Globe and Mail reporter Graeme Smith, who has reported extensively on Afghanistan, told CTV News Channel that Canada definitely has a poor reputation in parts of the war-ravaged country because of the torture issue.

"All these people are getting tortured, it's not a secret in Kandahar. Everybody knows about it," Smith said during an interview on Thursday morning.

"And so, that hurts our reputation and makes it harder to win the war."

Colvin says he filed repeated reports to Ottawa about the torture issue, though the most senior members of the government say they did not see them in 2006.

Colvin said he and other diplomats were discouraged from filing paper reports, which were often revised to the point where they could "no longer write that the security situation in Afghanistan was deteriorating."