NDP Leader Tom Mulcair and Justin Trudeau's Liberals are accusing the Harper government of misleading Parliament after Monday's revelation that Canadian Forces advisers exchanged gunfire with ISIS in what may be the first confirmed ground battle involving Western forces in northern Iraq.

"I asked the prime minister straight up in September whether this was a combat mission, whether Canadian troops would be involved in combat. I got a categorical answer, and the answer was no," Mulcair told reporters during an event at a Toronto child-care centre Tuesday.

"I specifically asked him in the House of Commons whether or not Canadian Forces would be targeting troops on the other side," Mulcair said. "He did not tell the truth."

During a briefing in Ottawa on Monday, Brig.-Gen. Michael Rouleau, the commander of the Canadian special operations forces command, revealed that Canadian Forces trainers working with Iraqi troops came under "immediate and effective mortar fire" from ISIS and responded with sniper fire, "neutralizing the mortar and the machine-gun position."

The troops had been in a planning session several kilometres behind the front lines, Rouleau said, but had moved up for a better view of what they had discussed.

He characterized the exchange of gunfire as consistent with the inherent right of self-defence and suggested an incident like this wouldn't have been unusual even in past Canadian peacekeeping missions.

Brig.-Gen. Michael Rouleau explains how Canadian special forces operators came under fire in Iraq. 1:17

"We have always been clear that while this is a low-risk mission, it is not without risk and our forces on the ground will protect themselves if fired on in the course of carrying out their mission," Prime Minister Stephen Harper's spokesman Jason MacDonald said in a statement Monday.

'Mission creep'

Liberal MPs gathered in London, Ont., for a caucus retreat this week echoed Mulcair's concern that the government needed to clarify the exact role Canadian troops were playing on the ground.

"The prime minister made assurances to Canadians and to the House that, as we found out yesterday, were not exactly the truth," Liberal Leader Justin Trudeau told reporters Tuesday.

"The prime minister needs to come clean with Canadians on what's going on and why he was lacking in forthrightness with Canadians."

"The government is going to argue obviously that this is not a combat mission in the sense of Canadian soldiers going on the offensive," said foreign affairs critic Marc Garneau.

"They are clearly on the lines, in some cases directing airstrikes, and this is something I think many Canadians did not realize," he said. "I think for some people yesterday that was a surprise."

In September, during a House of Commons foreign affairs committee hearing, Garneau specifically asked Defence Minister Rob Nicholson if he would confirm "that no Canadian soldiers will be in the trenches on the front lines, or taking part on the ground in any offensive or defensive operations."

Nicholson responded: "I've indicated they are not taking a combat role. Their role will be strictly advice and technical assistance."

When Parliament voted last fall on the deployment of aircraft for a bombing mission, Liberals were not supportive, suggesting the appropriate Canadian role to counter the ISIS threat would focus more on humanitarian assistance, training and logistics support.

"It has the appearance of mission creep," said defence critic Joyce Murray. "There appears to be a change."

No front-line role?

While information from Kurdish forces early on suggested Canadian trainers may call in airstrikes, Harper specifically said ground troops would not be accompanying the Iraqi forces into combat.

Now they've exchanged fire.

"The fact that it led so many newscasts indicates that Canadians were surprised — that we thought we were sending aircraft on a combat mission, on a bombing mission, and we suddenly find our ground forces are exchanging fire," said Liberal House leader Dominic LeBlanc.

"The government asked Parliament for a mandate for one sort of mission, and if they've decided now to do a different kind of mission, they should at least have the decency to come back and force their own MPs to vote in favour of the change of the mission," LeBlanc said.

Not every Liberal was surprised by Monday's revelation.

"Everyone expects that the Canadian military, even though they're there for the express purpose of training, if fired upon, they have to defend themselves. And it wasn't an aggressive stance, it was a defensive stance when fired upon and I think the public would be onside with that," said public safety critic Wayne Easter.

"We've asked for a review [of the mission] in six months," he said, adding that since Parliament made its decision, Liberals have supported the troops.

"We will see where we go at that point of time."

ISIS releases new video desc: Group threatens to kill 2 Japanese hostages unless it receives $200M US in 72 hours 9:29

In a statement circulated by the Conservative Party, Infrastructure Minister Denis Lebel said that over the past few weeks, jihadists have been shooting at Canadian soldiers. Because the soldiers fired back, the media now "pretends" that the Canadian mission has turned into a ground combat mission, he said.

"Canadian special operation forces must sometimes get close [to] or at the front lines. However, they spend 80 per cent of their time well back of them. This is not a ground combat mission," he said.

"When our soldiers are facing fire from [ISIS] jihadists, they must be able to respond," said Harper's senior Quebec minister.