OTTAWA - Concerns about the treatment of Afghan prisoners prompted Canadian soldiers to halt the transfer of detainees three times over the course of the last year, says Defence Minister Peter MacKay.

The suspensions are proof that agreements aimed at treating detainees humanely are working, MacKay said Monday.

The assurances came as the government and Defence Department prepared to counter explosive accusations from a Canadian diplomat that senior government officials turned a blind eye to the torture of Afghan prisoners transferred into the hands of Afghan authorities.

That counterattack will include a highly anticipated appearance Wednesday before a parliamentary committee by former chief of defence staff Rick Hillier, who was ultimately responsible for Canada's mission in Afghanistan.

Also scheduled to appear are Maj.-Gen. David Fraser, who led troops on the ground in Kandahar, and Lt.-Gen. Michel Gauthier, who was responsible for overseas deployments in 2006.

David Mulroney, who headed the prime minister's Afghanistan task force at the time, has also flown back to Canada from Beijing, where he is Canada's ambassador to China, and is asking to testify on Thursday.

In a pre-emptive strike, Mulroney wrote a Conservative MP to refute allegations that he was instructed by superiors to stop filing written reports on the treatment of detainees.

Liberal foreign affairs critic Bob Rae accused the government of trying to shut down the controversy with "fly in" performances by Mulroney and the generals before opposition parties have a chance to pore over all government documents related to Afghan detainees.

Rae said that whether or not the opposition allows Mulroney to testify on Thursday depends on the government's willingness to share documents.

Without those documents, which the NDP and Liberals demanded Monday, Rae said little can be accomplished by the committee hearings.

The government on Monday acknowledged the suspensions of prisoner transfers to Afghan authorities for the first time, even though opposition parties have been asking questions about the treatment of Afghan detainees for months.

MacKay said the suspensions followed the refusal by Afghan authorities to abide by an agreement that guaranteed access to prisons where the detainees were being held.

"Most recently the reason that the transfers stopped was that the Afghan officials were not living up to ... expectations," MacKay said during question period in the House of Commons.

He told Liberal Leader Michael Ignatieff that the government acted as soon as "credible allegations came to our attention."

"With respect to the pause in operations of transfers made on the ground in Afghanistan, it was because we could no longer have unfettered, unannounced visits to Afghan prisons.

"When Afghans are not living up to their obligations, we pause transfers. When they start to allow that access again, the transfers then began again."

MacKay bore the brunt of opposition attack Monday. Prime Minister Stephen Harper, who has not yet taken a question on the detainee issue, chose not to attend question period. His sole public appearance was a photo opportunity where he accepted a jersey from the national lacrosse team and took no questions.

Ignatieff accused Harper of ducking questions on the issue.

"It's significant that the prime minister was at a photo op, a kind of a hop, skip and a jump from Parliament Hill, instead of being in the House responding to questions that Canadians want answered because they're questions about his leadership."

The Conservative government has been on its heels since diplomat Richard Colvin told a Commons committee last week that prisoners handed over to Afghan authorities by Canadian soldiers were tortured, despite his repeated and explicit warnings about the mistreatment.

Conservatives have called Colvin's testimony "simply not credible."

Colvin suggested senior Canadian officials tried to suppress written reports about the treatment of detainees.

Mulroney denied the allegation in a letter to Conservative MP Rick Casson, chairman of the special committee on the Afghan mission.

"I can also assure the committee that I encouraged officials to report freely and honestly, while expecting them to meet the highest standards of accuracy, objectivity and professionalism," Mulroney wrote from Beijing.

Mulroney said Canada is at the forefront of detainee monitoring and always recognized that "the human-rights situation in Afghanistan was cause for concern."

And he backed the work of Canadian civilian and military officials "to put in place a very robust system to assist Afghanistan in meeting its ... commitments for the humane treatment of detainees."

Foreign Affairs Minister Lawrence Cannon said Monday that Colvin exercised his prerogative as a whistleblower in making the allegations.

But Cannon, who was in Kabul last week, stuck to the Conservative government line that the allegations have not been proven.

Nevertheless, he and MacKay said a new transfer protocol is in place and the government is "pleased" with the way it is working.

"Our government put in very tough regulations enabling the employees of the government through our whistleblower legislation to be able to come forward and make their comments known," Cannon said.

"Mr. Colvin has exercised his prerogative in that regard and, in this case, his allegations are not proven."

"The parliamentary committee is working, so we'll wait until the parliamentary committee has completed its findings."

Meanwhile, New Democrat MPs submitted a motion at the Afghanistan special committee to demand all government documents relevant to the torture of Afghan detainees, including Colvin's reports.

"The government is hiding the truth, and making a mockery of this committee, by refusing to release the documents it has in its possession," said the NDP foreign affairs critic, Paul Dewar.

"Conservatives have quashed access to information on this file since Day 1. The committee has clear powers to shed light on these documents and we fully intend to exercise our right to know the facts."

Liberals have also demanded the documents be released.

An Afghan agency, at one time entrusted to monitor Canadian-captured insurgents in Kandahar, says it has documented nearly 400 cases of torture across the war-ravaged country.

In its latest report, the Afghanistan Independent Human Rights Commission said it uncovered 47 cases of abuse in Kandahar, which it ranked third in the country.

"Torture and other cruel, inhuman or degrading treatment are common in the majority of law enforcement institutions, and at least 98.5 per cent of interviewed victims have been tortured," said the commission's April 2009 study.

The independent study, which tracked abuse claims between 2001 and early 2008, found the vast majority -- 243 -- were levelled in 2006 and 2007.

That is the time frame when Colvin was in Afghanistan and warning the federal government about torture.