Prime Minister Stephen Harper will ask Parliament to expand and extend Canada's role in the fight against Islamic State militants, raising the possibility of a push into Syria in a mission that has already become increasingly complex.

The announcement, which comes less than two weeks after the death of a Canadian soldier in Iraq, sets the stage for a divisive debate in the House of Commons next week. Opposition MPs are calling on Mr. Harper to better define Canada's mandate amid concerns that Ottawa could be drawn into another lengthy conflict like the decade-long war in Afghanistan.

The government has not said what an expanded mission might look like, but possibilities include allowing Canadian fighter jets to conduct air strikes in parts of Syria, bolstering support for air strikes in Iraq and increasing the number of soldiers training security forces in northern Iraq. Ottawa has also not said how long the next extension might last, but another six-month commitment would expire around the same time as the next federal election, offering an incentive to pursue a longer mandate.

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"The current mission was authorized in the fall and that authority comes due fairly shortly," Mr. Harper said at an event in Mississauga on Wednesday. "Next week, it is the government's plan to move forward with a request for Parliament for extension and expansion of the mission, and I will obviously give more details when we do that."

Asked specifically whether he would be open to expanding the fight against Islamic State militants into Syria, Mr. Harper said he would address the issue when the proposal is brought forward next week. While some members of the U.S.-led coalition have targeted militant operations in both Syria and Iraq, Canada's participation has been limited to Iraq alone.

"Let me just say that the current authorization laid open the possibility of going to Syria, although we have not done that," Mr. Harper said, referring to last fall's debate over the mission in the House of Commons.

At the time, the government indicated that Canada's combat mission would begin by targeting Iraq, but could eventually expand to Syria if Ottawa had the "clear support" of that country's government. The United States and its allies in the Persian Gulf have conducted air strikes against Islamic State militants in Syria, where President Bashar al-Assad is fighting IS and armed opposition groups.

IS militants control a large swath of territory on both sides of the Syria-Iraq border, covering an area that extends from Aleppo in Syria to Mosul and the Tigris River valley in Iraq.

Retired colonel George Petrolekas, a fellow with the Canadian Defence and Foreign Affairs Institute who has served in Bosnia and Afghanistan and with NATO, said the decision by some coalition members to conduct air strikes in Iraq – and not in Syria – has complicated efforts to combat IS extremists. "That entity has been cut in two based on an internationally accepted border that has no relevance on the ground," he said, referring to the Islamic State.

Any decision to expand Canada's role into Syria would likely be limited to the eastern part of the country, Mr. Petrolekas said, a geographic distinction that could help Canada stay away from Syria's broader civil war.

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Canada's mission in Iraq has grown increasingly complex in recent months, with the growing involvement of Iranian-trained militias and the recent death of a Canadian soldier. Sergeant Andrew Doiron was shot and killed this month when Kurdish allies fired on his special forces team as they returned to an observation post.

NDP Leader Thomas Mulcair said Wednesday that he would oppose any involvement of Canadian troops in "what is simply not our war" and suggested there are other places in the world where Canada can help people who are in trouble.

The Liberals said Canada has a role to play in battling Islamic State militants, but said Mr. Harper had not been honest in his portrayal of the Canadian Forces mandate.

Last fall, the NDP and Liberals both voted against the combat mission in the House of Commons, saying Canada should do more to improve humanitarian aid to help civilians in the region and resettle refugees. The Conservative majority in the House of Commons ensured the motion's passage.

The government does not require Parliament's approval for a renewed commitment in Iraq.

Canada's military contribution to the fight against Islamic State militants in Iraq includes six fighter planes, two surveillance aircraft and an aerial refuelling tanker. In addition, 69 special forces soldiers are assisting Iraqi security forces on the ground in northern Iraq.

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With reports from Daniel Leblanc in Ottawa and Ian Bailey in Burnaby, B.C.With reports from Daniel Leblanc in Ottawa and Ian Bailey in Burnaby, B.C.