Canada's top general says he didn't foresee that Canadian special forces troops would be directing air strikes in Iraq when he publicly ruled out this role during interviews last fall.

General Tom Lawson, Chief of the Defence Staff, told MPs at a House of Commons committee Thursday that "we're seeing an evolution in the mission" for 70 military advisers in Iraq.

Canadians have come under fire three times in Iraq and fired back, killing Islamic State militants, and are now directing air strikes on the ground for U.S.-led coalition fighters.

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Gen. Lawson nevertheless rejected the notion that Canada's ground troops are engaging in combat, which the government had said would not be part of the mission to upgrade the military skills of Kurdish fighters.

The senior officer's reasoning relies on fine distinctions.

Gen. Lawson said Canadian troops are not accompanying Kurds into combat but are nevertheless assisting their combat mission against Islamic State forces. Canada's special forces soldiers, who are armed, spend 20 per cent of their time near the front lines but are not looking for a fight.

He said Canadians are helping the peshmerga "heighten the accuracy" of their weapons.

For Canadians to be in combat, the general said, they would have to be at the front lines "with the troops that you have been assigned to, with your weapons being used to compel the enemy."

Asked to explain why Canadian soldiers now find themselves forced to defend themselves against firefights, Gen. Lawson said the fight is changing. Kurds are now taking the skills passed on by Canada and "putting pressure" on Islamic State militants.

Last fall, he told CTV News that soldiers would not be guiding air strikes from the ground in Iraq but would stick to training Kurdish peshmerga.

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But Gen. Lawson explained Thursday that he ruled out a role for Canadians as "tactical air controllers" in October because he figured this would require them to be on the front lines to direct airborne bombs.

He said it turned out that Canadian soldiers can direct air strikes from relative safety in Iraq.

"When I made my comments in October, that was based on 15 years as a fighter pilot working with tactical air controllers. These tactical air controllers I had worked with had always been on the very front" of the conflict, Gen. Lawson said.

"What I had not anticipated at that time … was that those tactical air controllers would be able to develop techniques that would allow them from the relative safety of their advise-and-assist positions to be able to help the peshmerga Iraqi security forces bring the weaponry of bombers, coalition bombers, to bear."

The opposition, which charges that Ottawa is incrementally transforming what is supposed to be a "non-combat" mission, accuses the government of splitting hairs.

Gen. Lawson, however, said that combat operations, in military doctrine, means operations where "the use of force is essential to accomplish a mission."

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In Iraq, however, the senior officer said Canadian troops are "carrying weaponry, but they are only used in self-defence."

NDP foreign affairs critic Paul Dewar told the committee that Ottawa's playing a game of semantics over whether the special forces are in combat and it's confusing Canadians.

Defence Minister Rob Nicholson shot back that he believes the NDP would prefer Canada stay out of the conflict.

He said Canadians will continue directing air strikes from the ground and firing back if attacked.

"Our special forces personnel are not at any time seeking to engage the enemy," Mr. Nicholson said.

The U.S. military says Canada's military advisers are the only coalition forces it knows of that have engaged in firefights with Islamic State militants in Iraq and that American troops have not, to date, been authorized to direct air strikes from the ground as Canadians are doing.