The opposition is challenging Prime Minister Stephen Harper to "make the case" for a combat mission in Iraq, as the federal government appears ready to step up Canada's role in the fight against Islamic State militants.

Sources tell CTV鈥檚 Ottawa Bureau Chief Robert Fife that Canada鈥檚 role in the Iraq mission will be announced on Friday, with a debate and vote in the House of Commons following early next week.

Both and emerged from their weekly caucus meetings Wednesday to decry what they call the government鈥檚 secrecy about what it plans for Canadian Forces in Iraq.

The government is currently considering whether to renew the current 30-day non-combat advisory mission to northern Iraq, which began on Sept. 5. Harper has said that any plan to send Canadian Forces into combat will be put to the House for a debate and a vote. That decision, he said Tuesday, will come "in days."

 鈥淭he situation in that part of the world is very serious, and if it is allowed to fester, it represents a serious danger to the national security of the country,鈥� Harper said in the House of Commons Wednesday.

Trudeau said Wednesday that Harper appears "intent on sending Canada into war in Iraq, and it's up to him to make the case for it."

Trudeau told reporters that he is 鈥渄isappointed with the secrecy and lack of forthrightness鈥� in the government鈥檚 answers during question period on a potential combat mission.

Mulcair said Canadians are "horrified鈥� by the atrocities committed by ISIS, but "the question is, what is the best way for Canada to react?"

Hundreds of thousands of Iraqis will be in need of humanitarian assistance as harsh winter weather descends on the region, he said.

"We've got to be extremely careful before we start listening to the siren song of those who would lead us into war," Mulcair said.

Both leaders declined to say whether they would whip the vote if the government made the vote on a combat mission a matter of confidence.

However, a source tells CTV that the NDP will likely vote against going to war.

Meanwhile, Canada's current advisory mission appears to be smaller than the government has claimed. The Canadian Press reported Wednesday that Foreign Affairs Minister John Baird informed the NDP in an email that only 26 special operations forces had been deployed to northern Iraq.

The government had responded to questions in the House about the mission by saying that 69 special ops are on the ground.

A government official, who spoke to CP on condition of anonymity, said fewer soldiers than first thought were required for the mission.