Afghan security police stand guard at a prison in Kabul. Richard Colvin, a former Canadian diplomat in Afghanistan, has testified that detainees transferred by Canadians to Afghan prisons were likely tortured by Afghan officials. (Musadeq Sadeq/Associated Press)

A parliamentary committee should not block testimony from officials willing to respond to allegations that detainees were tortured in Afghan prisons, Prime Minister Stephen Harper said Tuesday.

David Mulroney, who used to run the government's Afghanistan Task Force and now is Canada's ambassador to China, has said he wants to rebut the testimony of diplomat Richard Colvin.

Colvin told a parliamentary committee last week that all detainees transferred by Canadians to Afghan prisons were probably tortured by Afghan officials.

Prime Minister Stephen Harper says a parliamentary committee should not block testimony from officials willing to respond to allegations that detainees were tortured in Afghan prisons. (Fred Chartrand/Canadian Press)

"The diplomat in question, as everyone knows, has a right to his opinion and has given us his opinion," Harper told the House of Commons.

"We also know that a large number of his colleagues didn't agree with those opinions and … they have asked for their right to speak, so I’d encourage the opposition not to muzzle them."

But Opposition MPs have said they do not want to hear from Mulroney yet, saying they want the government to release documents related to the torture allegations before he appears.

MPs are seeking cabinet minutes from that time period, all memos sent from Colvin and returned to him and human rights reports given to the Defence Department.

Harper said Tuesday the government "has and will continue to make all legally available information available."

But during question period, Bloc Québécois Leader Gilles Duceppe said "we'll hear from witnesses when we have documents, non-redacted documents. We don't want redacted documents."

Colvin has also said that his concerns were ignored by top government officials and that the government may have tried to cover up the issue. Colvin further maintained that Mulroney told him to keep quiet about the situation.

Since then, the government has attacked the credibility of Colvin's testimony. Defence Minister Peter MacKay has claimed that Colvin's statements "cannot be sustained."

Liberal Leader Michael Ignatieff said the prime minister must have known about the torture allegations because of the "cascade" of reports in 2006 and 2007.

"It defies belief that this information never reached the prime minister," Ignatieff told the House of Commons.

"How can anyone believe that the prime minister did not himself know about torture in Afghan jails and the risk that detainees transferred there would be tortured? … How can he possibly justify his failure to act?"

But Harper dismissed the accusation.

"The fact of the matter is that whenever Canadian diplomats or Canadian military officials have concrete evidence, substantial evidence, of any kind of abuse, they take appropriate action."

Meanwhile, Brig.-Gen. Jonathan Vance, commander of coalition troops in Kandahar, said there was no risk of torture during his tenure.

"I determined that I would halt prisoner transfers, or detainee transfers, at any time that I thought there was any chance at all of a real risk to those detainees at the hands of the [National Directorate of Security]," Vance said in an interview after landing in Edmonton on Tuesday.

"On each of those occasions there was no real risk. The halt was simply to confirm that in fact the [Afghans] continued to comply with the agreement with Canada."

There was one occasion when Canadian troops did not have unrestricted access to these prisoners as requested, but that was quickly rectified by the Afghans when it was brought to their attention, Vance said.

Rick Hillier, the former defence chief, is to appear before the committee Wednesday, where he's expected to rebut a claim that he was warned that his troops were turning over detainees to torture in Afghan jails.

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.

Hillier has said he doesn't remember "a smoking gun" of the sort Colvin described. The retired general has said there were always concerns about transferring people to Afghan control, but he doesn't remember such a pointed warning.

With files from The Canadian Press