An Afghan man walks through a poppy field in the Nangharhar province of Afghanistan. (Associated Press)

Canadian soldiers in Afghanistan will be ordered to attack opium traffickers and drug facilities when there is proof of direct links to the Taliban, CBC News has learned.

The new order follows a heated debate among NATO allies over whether the attacks could be declared war crimes.

Defence Minister Peter MacKay told CBC News soldiers would indeed target drug traffickers and their production facilities.

"We're not going specifically to eradicate poppy crops, but we would go after proven drug traffickers with operations linked to the terrorists," he said.

MacKay, who is rumoured to be a candidate for the post of secretary general of NATO, said Afghanistan's police force will continue to have responsibility for "ordinary … criminals."

"What we're trying to do is step up our activity to cut off the linkage that allows for the supply of this explosive material that has been so deadly and so devastating.

"There is no question that there is direct linkage between the funding of terrorist activity and the poppy crop and the funds that are elicited from that poppy crop."

Commanders on the ground will decide whether Canada has the means to carry out individual operations aimed at drug traffickers, and all will meet Canada's legal obligations, MacKay said.

The plan was criticized in Parliament on Friday.

"Does the government believe that such military action will resolve the drug problem in Afghanistan and does the government support NATO orders that potentially put our soldiers at risk of violating international law?" NDP Foreign Affairs critic Paul Dewar asked.

Dewar said that the drug operation is not the kind of work Parliament approved when Canada's mission in Afghanistan was extended until 2011.

More than 2,500 Canadians are serving in Afghanistan's southern Kandahar province, a volatile region where Taliban-led attacks against foreign troops are frequent. British, Dutch and American troops are also in the southern area as part of a multinational NATO-led task force.

NATO backs decision, says chief

The issue had divided the 26-member military alliance.

Commanders on the ground had earlier refused an order from the organization's top commanders to target the drug trade because the NATO order failed to distinguish between drug traffickers and those who directly support the Taliban.

International law forbids nations from using military force against criminals, including drug traffickers.

Drug traffickers with links to the insurgency could be considered a legitimate target.

The attacks would be legal if intelligence can prove links to the Taliban, said Payam Akhavan, a former UN war crimes prosecutor who now teaches at McGill University in Montreal.

"The question of burden of proof really revolves around intelligence gathering," Akhavan said.

NATO Secretary General Jaap de Hoop Scheffer said Thursday there is "full agreement" within NATO's chain of command on the decision.

"We have full agreement … that we can go indeed after laboratories where the poppies are brought in and turned into heroin … or after the guys and the people who bring in the precursors," he said.

So-called precursor chemicals are materials that help refine opium into heroin.

"NATO will not act outside international law. This nexus between the insurgency and the narcotics business leads to the killing of our soldiers in Afghanistan," he said.

"That really is a price too high to pay for our soldiers."

With files from James Cudmore