Canadian snipers on the front lines in Iraq have once again killed Islamic State militants during their non-combat mission advising Kurdish forces – part of an evolving role for this country's soldiers as the battle accelerates to win back the northern city of Mosul.

On Monday, the Canadian Armed Forces announced this country's special forces soldiers had twice exchanged fire with the enemy in Iraq in the last week, bringing the total number of such clashes with Islamic State extremists to three.

The military says in the latest two instances Canada's troops were "examining the terrain" near the battlefront as part of their work as military advisers to Kurdish peshmerga when they came under attack and fought back in self defence. It's similar to the explanation given for the first incident in mid-January.

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In all cases, Defence officials say, it was Canadian snipers who returned fire and "neutralized the threat," a phrase sources say means they killed enemy fighters. The military would not say how close Canada's soldiers came to Islamic State forces, but the effective range of the C-14 Timberwolf sniper rifle, one of those used by this country's troops, is 1,500 metres.

These encounters with Islamic State forces, as well as last week's revelations that special forces soldiers have directing air strikes against ground targets in 13 cases, represent an expansion of Canada's ground activities in the conflict and pose a challenge for a Conservative government that sent troops on the understanding their actions would be limited to advice and training.

The Conservatives struggled Monday to paper over contradictions in what Canadians have been told about the mission facing nearly 70 special forces soldiers and to allay concerns raised by rivals that this country's troops may be drawn deeper into the conflict and risk casualties. The military now says Canada's troops spend about 20 per cent of their time near the front lines as part of advising and training the Kurds.

In September, Prime Minister Stephen Harper defined the military advisory mission quite narrowly.

"If I could just use the terminology in English, it is quite precise. It is to advise and to assist. It is not to accompany," Mr. Harper told the Commons.

On Monday, however, Defence Minister Rob Nicholson offered a more expansive definition of Canada's ground role.

"I am not sure we could train troops without accompanying them. We have been very clear that we would be in the business of assisting and training these individuals."

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NDP Leader Tom Mulcair called on the Conservatives to concede Canada is now in ground combat.

"Last fall, the Prime Minister specifically said that Canadian Forces would not be pinpointing targets on the ground. The Chief of the Defence Staff agreed that it would be a semi-combat role and it would not fit with a non-combat mission," Mr. Mulcair noted.

Liberal Leader Justin Trudeau said he supports the right of Canadian soldiers to defend themselves when under fire but adds it's unexpected to hear these military advisers are now "routinely on the front lines."

Mr. Nicholson said the Conservatives don't believe in leaving the "heavy lifting" to others. "That has never been the Canadian way for 200 years." We do not stand on the sidelines, we get out there and we stand up for those who are oppressed."

David Perry, a Conference of Defence Associations Institute analyst, said what's happening to date cannot be considered a dramatic shift in role, pointing out the rules of engagement for Canadian troops have not changed. He said the forces that Canada is advising are heading toward Mosul to help liberate the Iraqi city and as they reclaim territory, they and their advisers are encountering tougher fights.

"If this is ground combat, then how come we are hardly ever doing it? I would imagine it would be a hell of a lot more than three firefights and 13 involvements in air strikes."

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As the fight intensifies in Iraq, the Islamic State is threatening more violence against the West. A spokesman for the extremist group on Monday called on Muslims living in Western countries to carry out more attacks, saying any loyalist who has the opportunity to "shed a drop of blood" should do so. "You all saw what one Muslim did in Canada and its infidel parliament," Abu Mohammed al-Adnani, said in a nine-minute recording, referring to the October attack in Ottawa.

Roland Paris, director of the Centre for International Policy Studies at the University of Ottawa, said mission creep is under way.

"The U.S. military indicated last week that American troops currently in Iraq are not being deployed with Iraqi units to front-line positions. Rather, they are training Iraqis behind the wire at four major military bases. The assertion that deploying Canadian troops to the front lines is an inevitable element of advising and assisting is, therefore, misleading," he said.

With reports from The Associated Press