The Conservative government is arguing that waging war is part of a humanitarian response to the suffering caused by Islamic State militants, as Canada prepares to expand its combat mission into Syria.

Defence Minister Jason Kenney, whose party has arranged a Commons vote next week to give this continued deployment the stamp of legitimacy, tried a different tack in explaining the military action Thursday as MPs debated a motion that would endorse the Canadian Armed Forces fighting in Iraq – and now Syria – through March, 2016.

Both major opposition parties oppose the combat role in this mission and argue Canada's modest resources would be better spent funnelling humanitarian assistance to the millions of people displaced by Islamic State forces.

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The Conservatives have produced a revolving series of justifications this week to explain the mission, from the argument that Islamic State forces have called for attacks on Canada, to the need to protect Iraq from jihadis seeking a haven in Syria, to the risk that radicalized Westerners fighting there will one day return to terrorize Canada.

Mr. Kenney challenged the heart of the opposition parties' position Thursday, arguing that Canadian troops and jet fighters are an instrument of humanitarian assistance because the air strikes and training of Kurdish fighters are helping to degrade the effectiveness of the Islamic State of Iraq and the Levant (ISIL) and ultimately preventing more violence.

"The [opposition] member talks about humanitarian relief. The point of our military operation is to prevent more internally displaced persons, more refugees, more victims and more genocide. Does the member not understand that had we not begun this military operation several months ago there would have been thousands, perhaps tens of thousands of additional victims of ISIL's genocide?" the Defence Minister said.

"If the responsibility to protect means anything … does it not mean in an instance such as this, preventing genocide, preventing ethnic cleansing, preventing sexual slavery of women and preventing the execution of gay men by throwing them off towers?"

The Official Opposition NDP opened the debate Thursday by proposing rewriting the Commons motion to have Canada cease all combat operations in this deployment and refocus on delivering aid to those victimized by Islamic State forces.

NDP foreign affairs critic Paul Dewar said Canada could make a far greater impact if it took the money it's spending on the military mission – estimated to total $122-million for the first six months of the deployment – and spent it on feeding, clothing and accepting refugees.

He said the air strikes would be taking place regardless of whether Canada contributed six jet fighters.

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"They just want to look like they're doing something big, in the skies and with boots on the ground, instead of doing the most responsible and effective thing that Canada can do," Mr. Dewar said of the Conservatives. "The truth is that most of those in need in Iraq are not in ISIS-controlled territory; they are refugees, internally displaced persons and people whose livelihoods have been stolen from them by chaos and carnage. These are victims of ISIS, and Canada can help them now."

The United States has been conducting air strikes with a number of Middle East allies in Syria for about eight months while other western countries have limited bombing raids to Iraq, which has invited NATO countries and Arab allies to come to its aid. Syria, which has lost control over its eastern territory, has not actively opposed the incursions to fight the common enemy.

Canada will be the only other Western country joining the United States in waging war in Syria, ruled by the Assad regime, which has become an international pariah because of a murderous war waged on its civilians.

It's possible that the Canadian military may already have been contributing to the air strikes in Syria because the Canadian aerial refuelling plane is available for all coalition planes to use, including American fighters performing bombing raids against Syrian targets.

One military analyst predicted Canadian warplanes will likely end up finding fewer targets in Syria because there will be less ground support to ensure the risk of civilian casualties is zero. Canada has a no-civilian casualty policy when selecting bombing missions in Iraq, and this has already limited its choice of sorties there.

"Our desire to take every precaution and make sure there aren't any civilian casualties might make it harder to find targets we can engage in Syria because the situation there is a little bit more complicated," said David Perry, a senior analyst with the Canadian Defence & Foreign Affairs Institute.

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The Conservative government tried to allay opposition criticism that it hasn't boosted aid delivery to the region to match this planned expansion of combat by saying this additional support will come.

"I can assure Canadians that our government intends to provide large-scale humanitarian and stabilization assistance to help alleviate the suffering this terrorist group is inflicting," Foreign Affairs Minister Rob Nicholson told the Commons. "But in order for this assistance to be effective, we must degrade ISIL."

Mr. Nicholson acknowledged Canada could be helping the Assad government by fighting a common enemy, but feels the overriding goal remains beating back the Islamic State, which moves with ease between Syria and Iraq, where Canada has participated in air strikes against militants since last October. He said Canada is not blind to the fact it's inadvertently on the same side as organizations with which it has nothing else in common.

"The expansion of our air strikes in Syria in no way legitimizes or strengthens the murderous campaign of Syria's dictator Bashar al-Assad, nor does it mean that we are naive about the ambitions that the clerical dictatorship of Iran harbours through their Shia militias in Iraq, and the presence of the Hezbollah and [Islamic Revolutionary Guard] fighters they sponsor in Syria. Our air strikes in Syria have one goal and one goal only: to degrade ISIL."