Liberal opposition MPs continued to hound Defence Minister Gordon O'Connor on Thursday to release information regarding Afghan detainees captured by Canadian forces, but he said he won't co-operate because the issue is "a matter of national security."

During question period in the House of Commons, O'Connor reiterated what he said on Wednesday before a joint meeting of the parliamentary committees on national defence, and foreign affairs and international development.

"We do not intend to do anything to impede military operations in Afghanistan," he told the Commons.

Leading the latest attack was Ontario Liberal MP Ruby Dhalla, who accused the Conservatives of a coverup.

"After repeatedly misleading this House, the ministers of defence, of foreign affairs and public safety were forced to admit there are two new detainee capture cases [involving abuse allegation]," she said. "Will the minister tell us how many detainees have been captured by Canadian forces or will they admit once and for all that they just do not know?"

Foreign Affairs Minister Peter MacKay told the Commons that Canadian officials have had "unfettered and private" visits to holding facilities in Kabul and Kandahar since reaching a new monitoring agreement last month.

On Wednesday, Public Safety Minister Stockwell Day told the joint parliamentary meeting that four prisoners have complained of mistreatment since they were captured by Canadian forces in southern Afghanistan, and that the Red Cross and Afghan Independent Human Rights Commission were investigating.

Day revealed news of the first two cases of alleged abuse in April.

No numbers of alleged abuses released

While both Day and MacKay were forthcoming with numbers on abuse allegations, no information has been released on how many prisoners Canada has captured while fighting the Taliban.

"The U.S. issues a press release about every detainee they capture," Dhalla said Thursday in a statement directed at O'Connor. "Why does this minister refuse to be as transparent?"

The defence minister said that in Afghanistan, each country involved in defence and reconstruction determines its own policies.

"In the case of Canada, the military has determined that the public release of information on detainees would be detrimental to their military operations," he said. "The operational chain of command has a responsibility for deciding what kind of information is releasable or not. It is a military decision, not a political decision."

Since the beginning of May, the U.S. military has issued 25 media releases detailing the capture of at least 100 Afghan prisoners.

Information in the releases is posted on a U.S. army website and includes:

• Where the captures occurred.
• The number and type of weapons seized.
• Information about the prisoners, such as rank and sometimes even names.