Chief of Defence Staff Tom Lawson says Canada's special forces aren't put into places where they expect to come under fire.

Speaking to MPs at the House foreign affairs committee, Lawson said despite spending 20 per cent of their time near the front lines, the special forces have had to return fire only three times.

"So although the risk is low, and we continue to think it is low in that role, it is not zero," Lawson said.

"We in no way put our special operations troops anywhere near where we believe they will come under fire."

Lawson was at committee to brief MPs on the fight against the Islamic State in Iraq and Syria (ISIS) with Foreign Affairs Minister John Baird and Defence Minister Rob Nicholson.

MPs questioned Lawson, Baird and Nicholson on the scope of the mission and whether Canadian soldiers are involved in ground combat, leading at times to some testy exchanges. Government MPs accused the opposition of not supporting the Canadian Armed Forces and NDP foreign affairs critic Paul Dewar at one point heckled Nicholson when he didn't feel Nicholson was answering his questions.

Defence officials recently revealed that special forces operators who had been described as working in an "advise and assist" role have actually exchanged fire with ISIS forces three times.

Not combat, top soldier says

On Thursday, NDP defence critic Jack Harris lodged a formal complaint against Prime Minister Stephen Harper for providing "misleading information" to the House of Commons on the scope of Canada's military efforts in Iraq.

Liberal MP Marc Garneau read the Canadian Armed Forces' definition of a combat operation, which includes the necessity of lethal force, and asked whether that is what the military is doing in Iraq.

"It is not," Lawson said.

The Canadian special forces operators, he said, are providing Peshmerga, the Kurdish forces with whom the Canadians are working, the ability to "heighten the accuracy of the weapons" used.

Accompanying troops has a different meaning in military doctrine than in normal language, Lawson added.

"In military terms, as you are quoting doctrine, it has a very clear other meaning. And that is that you are now up front, with the troops that you have been assigned to, with your weapons being used to compel the enemy. So there is no confusion with our special operators on that accompany role."

Calling in targets

Canadian officials have said the special forces are calling in, or painting, targets for the Iraqi forces, though Nicholson wouldn't say when that happened.

"This has been an evolutionary process, working with them right from the start," Nicholson said. 

"They're moving forward and that's what we are very, very proud [of]."

Harris said the real issue is whether Canadians were misinformed by the prime minister.

"Canadians have to be able to trust what they're told by the prime minister. If we see evolution, what we call mission creep and potential escalation, the question is what's next and what's this going to lead to. That's very concerning here when we don't really trust what this government is telling Canadians and telling Parliament."

The House of Commons voted in support of a six-month air bombing mission in October (the government doesn't need parliamentary approval to deploy the military).

The government committed 600 troops, one CC-150 Polaris air-to-air refuelling aircraft, two CP-140 Aurora surveillance aircraft, and the necessary air crews and support personnel. Canada also sent six CF-18 fighter jets and one dedicated airlift plane to enhance the refuelling, air surveillance and transportation capacity of coalition members.

Those are in addition to a commitment of up to 69 special forces troops who work on the ground with Iraqi forces.