Prime Minister Stephen Harper made his case for Canada to renew its participation in the coalition fighting the Islamic State in Iraq and Syria, but left some questions unanswered as the opposition leaders challenged him to provide more details.

The prime minister is proposing to expand and extend Canada's initial six-month military mission in Iraq and asking for support for an additional one-year air mission against ISIS.

That length of extension of the mission is significant. A six-month extension would have put any further renewal in the middle of next fall's election campaign. Canadians must go to the polls by Oct. 19, 2015.

With the debate officially underway, both NDP Leader Tom Mulcair and Liberal Leader Justin Trudeau referred to concerns the government wasn't honest about the role special forces operators were playing in Iraq, painting targets, or guiding airstrikes, for the Kurdish Peshmerga, whom they are training. They also raised concerns about whether there is an exit strategy.

Defence Minister Jason Kenney stepped up the end goal for the mission, upgrading from containing and "degrading" ISIS to defeating the violent insurgents.

"The ultimate objective is to defeat this organization so they can no longer pretend to be operating a state or a quasi state," Kenney said in an interview on CBC News Network's Power & Politics.

"The organization has attracted recruits and radicalized people by giving expression to this idea of the caliphate. We think it's hugely important to demonstrate to individuals who might be susceptible to radicalization that it isn't really a caliphate. It's actually a losing force."​

The expanded and extended mission will include:

The air combat mission — specifically air strikes, air-to-air refuelling, surveillance by the Aurora aircraft, and deployment of aircrew and support personnel.

Canadian Special Operations Forces (SOF) continuing their advise-and-assist mission with Iraqi forces combating ISIS.​

Prime Minister Stephen Harper makes his case for why the House should support extending Canada's fight against ISIS for a year and expanding into Syria from Iraq. 14:06 Canadian special forces won't be in Syria, Harper said in question period.

"In this motion, the government has no intention of having our special forces operate in Syria," Harper said in response to a question from Trudeau.

"They will continue operating in northern Iraq assisting Peshmerga forces there."

Legal basis for Syria unclear

However, Canada's contribution isn't limited to the Canadian Armed Forces, Harper noted in his speech Tuesday morning.

"We have also been helping to support more than 200,000 Syrian refugees in Iraq, with food, water, shelter and protection. There is no either/or here between military action and humanitarian aid. The situation desperately needs both and Canada has been vigorously providing both," he said.

When he initially made the case for joining the coalition fight in Iraq, the prime minister said Canada would strike ISIS "where – and only where – Canada has the clear support of the government of that country."

But that's no longer the case, he said Tuesday morning.

"In expanding our air strikes into Syria, the government has now decided that we will not seek the express consent of the Syrian government," Harper said, adding that Canada would work with allies who have already been operating in the air over Syria.

Mulcair used question period to ask pointedly for more details about the mission.

NDP Leader Tom Mulcair argues Canada should be focused on humanitarian aid and diplomacy in Iraq and Syria, not taking part in combat. 16:10 "What is the legal authority for bombing in that country?" Mulcair said.

Harper responded that it would be with the legal authority on which the U.S. and other allies have based their operations.

'Hasn't earned trust'

"Our allies have indicated they are taking necessary and proportionate military action in Syria on the basis that the government of Syria is unwilling or unable to prevent [ISIS] from staging operations and conducting attacks there, including ultimately attacks that include this country as a target," Harper said.

"That is the legal basis on which we are proceeding."

Trudeau asked how Canadian pilots would avoid having Syrian air defence weapons trained on them. Harper said only that Canada's allies are already doing that work, and referred again to Syria lacking either the will or the capacity to fight ISIS.

Mulcair argued in his speech Tuesday morning that Canada has "no place in this war," to a round of grumbling by the Conservatives. House Speaker Andrew Scheer was forced to interrupt twice to silence them.

"The prime minister hasn't earned that trust, because he misled Canadians from the start," he said, referring to the work of special forces operators.

Mulcair said if he were to be prime minister after the next election, he would end the mission.

The NDP and Liberals voted against the initial motion last fall.

Assad could consolidate 'grip on power'

Trudeau warned Canada's involvement in Syria could "very well result" in Syrian President Bashar al-Assad "consolidating his grip on power."

Liberal Leader Justin Trudeau says his party won't support a mission in Iraq and Syria without knowing the objectives and the exit strategy. 12:23 He said the government hasn't articulated the mission's objectives, or said how Canada will know whether it has achieved the objectives. He said there's no exit strategy beyond the stated end date a year from now.

"It is hard to believe the public timelines," Trudeau said, especially after Foreign Affairs Minister Rob Nicholson compared this war to the one fought in Afghanistan over a decade.

A spokeswoman for Trudeau said if he were to be prime minister after the next election, the Liberals would "change Canada's focus to training and humanitarian assistance as quickly and responsibly as possible."

Opposition parties received the text of the new motion on Monday night, and will be briefed further on Wednesday. The debate will likely begin on Thursday.

A Canadian prime minister does not need authorization from Parliament to launch a combat mission, but Harper has made it a practice to ask the House for support in those instances.

Polls suggest the Conservative government is playing a winning hand. Surveys indicate strong public support for the fight against ISIS.