Canadian Forces are holding about 18 or 20 Afghan detainees at their military base in Kandahar, an investigator with the Afghanistan Independent Human Rights Commission confirmed on Thursday.

Farid Hamidi, in an interview with CBC Radio's As It Happens, said that since Canada stopped handing over detainees to Afghan officials in November, they have been holding them on their own airfield.

The revelation comes as opposition MPs and human rights activists have been asking the Conservative government to disclose what the military now does with the prisoners it seizes in Afghanistan.

Media reports have suggested detainees were being held at the Kandahar base, but Prime Minister Stephen Harper has maintained it is up to the Canadian military to disclose any details about detainees.

Hamidi said Canadian officials have provided his organization with information directly.

"They sent to our office in Kandahar official letters about information about the detainees," he said, when reached by telephone in Kabul.

Hamidi said his commission will now ask for access to the detainees Canada is holding, and will want information about how the prisoners are treated, and the conditions of the prisons where they are being held.

The commission, which is funded by the countries involved in the NATO mission in Afghanistan, made a deal with Canada last year, agreeing to monitor the condition of all detainees seized by the Canadian military and handed over to Afghan officials.

Hamidi said the Canadian military initially didn't inform the commission that it stopped handing over prisoners. Canada quietly ended the practice on Nov. 6, a day after evidence emerged that a prisoner in Afghan custody had been beaten unconscious with an electrical cable and a hose.

News of Canada's decision to halt transfers only emerged in the media last week.

"The human rights commission did become aware of this just from the media," Hamady said. "We weren't informed."

Liberals grill Conservatives on detainee issue

Harper and his government were grilled on the issue of detainees in the House of Commons on Thursday. The Liberals demanded to know if, on joint operations, Canadian soldiers were stepping aside and letting the Afghan soldiers to take prisoners, allowing the Canadians to avoid having detainees in their own custody.

"Because this is not technically a transfer, the detainee transfer agreement does not apply, but beyond technicalities, there are the moralities," Liberal Leader Stéphane Dion asked Harper. "Is this happening, yes or no?"

Harper said there are going to be occasions where Afghan soldiers take prisoners.

"As we train the Afghan forces to take over more and more of the responsibility for their security operations, of course they will be taking on more and more responsibility for these various aspects of the security operation," Harper said.

Layton, U.S.  question whether war is winnable

Meanwhile, NDP Leader Jack Layton criticized the Afghan mission as a whole, calling it unwinnable. Although his party has long called for a withdrawal of Canadian troops, his message was bleaker than usual.

"It's an endless mission," Layton told reporters in Ottawa on Thursday. "No one has laid out, anywhere, that it's possible to ultimately win a war in this region. No one.

"And historical experience shows that it's been impossible — whether it be Alexander the Great, the British in the 19th century, or the Russians in the 20th century. We're saying, 'Let's recognize these historical realities.'"

Layton, who distributed a list of quotes from military officers and analysts to support his case, said he would ask Dion on Monday to help him outvote the government in any parliamentary move to extend the Afghan mission beyond February 2009.

"I'm very concerned that Mr. Dion may be considering supporting the direction of Mr. Harper," Layton said.

While the NDP criticized the mission, across the border, U.S. senators said they fear NATO is in danger of losing in Afghanistan.

During two hours of questioning at a committee hearing in Washington, D.C., senators from both parties grilled administration officials who argued there's been a lot of progress since the war began after the Sept. 11, 2001, attacks on the United States.

"We cannot afford to fail in Afghanistan," said Republican Senator Norm Coleman. "The mission is faltering."

With files from the Canadian Press and the Associated Press