Defence Minister Gordon O'Connor says a new provision has been added to Canada's prisoner transfer agreement with Afghanistan.

The news comes just days after news broke this week that three Afghan prisoners who are considered key witnesses in the probe into allegations of abuse by Canadian soldiers, have disappeared.

Speaking on CTV's Question Period on Sunday, O'Connor said Canada has signed an agreement that requires an Afghan human rights group to monitor treatment of detainees.

"What we've done is we've added to it recently. We've added another process getting the Afghan Human Rights Commission involved. We just signed another agreement with them at the local level," O'Connor said.

However, he said the agreement has been in the works since last June, and is not the direct result of the prisoners' disappearance.

The transfer agreement originally signed in 2005 by Chief of the Defence Staff Gen. Rick Hillier, stipulated that detainees will not face execution after Canadian troops hand them over. It also requires that "accurate written records accounting for all detainees" be kept by both Canada and Afghanistan.

But Canada has no power to follow up and ensure that the provisions are followed once the prisoners have been handed over.

Other forces, such as the Dutch, British and Danish, have such stipulations written into their handover agreements, but Canada's only sets out that the International Committee of the Red Cross is responsible for the treatment and tracking of the prisoners.

Now, he said, one more "level of comfort" has been added into the deal.

"We're there in support of the Afghan government and when we get insurgents who break the law we hand them over to the authorities," O'Connor said.

"We want assurances that they're treated in accordance with the Geneva Convention. I know according to the rules of law they don't have to be treated under the Geneva Convention, but we insist that they are. We are reliant on the International Red Cross to monitor this and now we're asking the human rights organization to also do it."

Suspected militants captured in Afghanistan do not fall under the Geneva Convention, according to the military, because they do not wear a uniform and are not fighting for a recognized state.

O'Connor refused to speculate on what may have happened to the three missing prisoners, but said no one should jump to conclusions until the National Investigation Service has completed its probe.

He pointed out that the families of Afghan prisoners often find the means to get them released.

"Theoretically, everyone is member of a tribe and sometimes tribes get their people out of prison either through influence or paying fines...so it's quite a revolving door," O'Connor said. But he added that "anyone can be found."

The disappearance of three Afghan detainees -- key prisoners in the investigation into alleged abuse by Canadian soldiers -- has prompted strong criticism over the prisoner handover agreement.

Critics say Canada is putting too much faith in the Afghan military to treat suspected militants with respect, claiming they are often subjected to torture and even execution.

"This is a tremendous failing on the part of the Department of National Defence and I worry about it," Amir Attaran, a law professor from the University of Ottawa, told CTV Newsnet on Friday.

"It's just minimal basic requirement of taking care of any living person that you treat them without any kind of risk of torture, that you shelter them properly and you do not give them to known torturers as the Afghans currently are."