Canadian troops supporting Kurdish allies have destroyed three explosive-laden vehicles with anti-armour missiles, senior military officials revealed Wednesday, as they started lifting the veil on what the country's forces are doing in Iraq.

Maj.-Gen. Mike Rouleau, commander of Canadian Special Forces Operations, told reporters the three suicide vehicles were charging the Kurdish lines and could have caused "mayhem" if they had not been destroyed.

"The Kurds do not possess weapons like we have," he said. "So our three engagements with anti-armour weapons systems prevented that from happening several thousand metres before they wanted to detonate."

The comments came amid an ongoing debate over whether Canadian troops in Iraq are involved in combat, which was further fuelled this week by revelations some of the more than 200 soldiers have shot first.

The Liberal government has been accused of hiding information and even misleading Canadians about the nature of the mission, after promising to end the combat mission in Iraq during last year's election campaign.

In March, they withdrew six CF-18 fighter jets that had been deployed by the previous Conservative government to bomb ISIS targets in Iraq and Syria.

But the Liberals tripled the number of special forces soldiers on the ground in northern Iraq to more than 200 from 69, even though they had insisted while in opposition that those troops were also in combat.

Military officers say Canada's "advise and assist" mission has evolved from primarily training the Kurds behind the lines to supporting Kurdish operations, but that the rules governing the mission have not.

Rouleau said Canadian troops are not leading the fight or engaged in any "offensive combat operations" as a unit against the Islamic State of Iraq and the Levant, or Daesh.

"We have never accompanied any leading combat elements," he said. "My troops have not engaged in direct combat as a fighting element in offensive combat operations. We do not plan on that basis, because our mandate does not allow us to do so."

Rules of engagement

Rather, he painted a picture of Canadian troops sitting on rooftops or hilltops with sniper rifles and other weapons, watching and ready to help Kurdish forces as they advance across the battlefield or civilians as they try to flee.

"From deliberately selected positions that maximize our utility to advancing Kurd forces, we have either defended ourselves, defended friendly forces, or defended civilians who are caught in the middle," Rouleau said.

"And we have done so with kinetic force against Daesh."

A former Ottawa police officer, Rouleau at one point compared the rules governing his troops in Iraq to those that dictate when a police officer can use lethal force.

"When confronted with a situation of serious bodily harm or death, a police officer does not have to wait to be stabbed. Does not have to wait to be shot at, in order to use force," he said.

"I think it's reasonable to conclude that we would not expect to deploy our soldiers overseas with any lesser ability to defend themselves than our police officers have in Canada."

Erbil pics

An unidentified Kurdish soldier looks out for ISIS fighters at the front on Zardek Mountain, northwest of Erbil. (Murray Brewster/CBC)

Conservative defence critic James Bezan said whether Canadian soldiers are advancing with Kurdish forces or supporting them with sniper fire from afar, the result is the same: they are in combat.

And he accused the Liberals of putting military commanders in an "uncomfortable position" by insisting that the mission be labelled non-combat.

"This is now strictly a supportive role, but it is a combat role," Bezan said. "We're okay with that. But the government should be open and transparent about what it is."