Liberal Leader Justin Trudeau is cautioning against sending Canadian jet fighters to join U.S. air strikes against the Islamic State.

U.S. President Barack Obama announced the air strikes against militants in Syria and Iraq in an address Wednesday night.

While Mr. Trudeau didn't completely rule out supporting such a move eventually, he said Canadians aren't enthusiastic about taking on such a "combat" role.

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"Shifting toward a combat mission, which air strikes would be, will require a large shift in Canada's positioning, and I just don't see a tremendous level of enthusiasm or openness among Canadians, or Canadian parliamentarians, for taking on a combat role in Iraq," he said.

So far, Prime Minister Stephen Harper has sent special forces advisers to assist the U.S. military in northern Iraq, but he has not made clear whether Canada will expand that role.

Foreign Affairs Minister John Baird and Defence Minister Rob Nicholson appeared before MPs at a special committee hearing Tuesday, where Mr. Nicholson described the sending of advisers as an "initial deployment" of troops.

The group that calls itself the Islamic State – formerly the Islamic State of Iraq and the Levant – seeks to impose a vicious interpretation of its religion on captured cities and has conducted mass killings of non-believers.

Mr. Trudeau warned against escalation of Canada's involvement in the conflict.

"Ten years ago, Mr. Harper was eager to send us into a combat role in Iraq, and we managed to avoid that. I think it would be a mistake to escalate our support. But there are many ways to support our allies, and we are and we should."

‎Mr. Trudeau, however, did not completely rule out sending jet fighters in the future, such as when Canada sent six CF-18s to take part in airstrikes in Libya in 2011.

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"I think that's something we could certainly talk about, but it would be an escalation of Canada's role right now. I truly believe that Canada's role needs to primarily be what it's been laid out as: humanitarian support for civilians, help on a refugee basis, but also providing training in a non-combat mission, non-combat role, to the local troops."