Defence Minister Rob Nicholson is defending a motion to have Canada join airstrikes against ISIS, arguing that the government has to take action against the extremist group that poses a "direct threat" to the country.

Following Prime Minister Stephen Harper’s announcement on Friday that Canada will join the U.S.-led airstrikes against Islamic State militants in Iraq, Nicholson said the country simply can't sit back while our allies fight.

"(ISIS) is a direct threat to Canada. As the United Nations and others have outlined, this terrorist organization is in the business of brutalization, rape and murders," he told CTV's Question Period. "So we have to take action and that's exactly what we're doing."

On Friday, Harper announced Canada will join its allies in an air campaign against ISIS for a period of up to six months, but will not deploy ground troops in combat operations. Harper said while the airstrikes will be limited to Iraq, they could possibly expand to Syria if the government there gives the green light.

A debate and a vote on a motion detailing the mission will be held in the Tory-dominated House of Commons on Monday.

CTV News has learned that Minister of Public Safety Steven Blaney, RCMP Commissioner Bob Paulson, and Canadian Security Intelligence Service Director Michel Coulombe will outline this week the direct threat radicalized Canadians pose to the public in this country.

All three are expected to appear before the public safety and national security committee on Wednesday, where they will speak about the growing danger of radicalization and reveal how intelligence officers and front line police are dealing with those concerns.

Although they have acknowledged the threat posed by ISIS, both the NDP and Liberals have already indicated that they will not support Canada’s combat mission in Iraq.

The mission will include up to six CF-18 Hornet fighter aircraft, surveillance and refuelling aircraft, and air crew and personnel.

Nicholson said he recognized there are concerns the initial six-month mission may be extended in the future.

"We always have to assess what we're doing and the resolution is 'up to six months,'" he said. "These things are never perfect, but we're on the right track.

"We're going to work in co-operation with our allies, and we want to send out the message that the activities of (ISIS) are completely unacceptable. It's unacceptable to Canada, and that's consistent with the traditions of this country."

Last month, Canada deployed special ops to Iraq to serve in a non-combat, advisory mission to help train Iraqi forces fighting ISIS. That mission was for 30 days and is in the process of wrapping up. The Conservative government said it will be extending the length of that mission.

NDP, Liberals call for humanitarian support

NDP Leader Tom Mulcair said he believes the Conservative government will "of course" be back in six months to seek an extension for the mission.

"If the Americans couldn't get the job done in a decade, we're not going to get it done in six months," he told CTV's Question Period.

Mulcair said Canada should be providing support to humanitarian efforts on the ground rather than participating in airstrikes.

The NDP did not support Canada's smaller, non-combat mission.

The Opposition Leader said while there is no denying all Canadians are horrified by ISIS, Canada should be learning from the mistakes of the past that have, in part, led Iraq to the situation it is in today.

"Before repeating errors of the past, let's learn from them," he said. "Let's get Canada doing the kinds of things we can do to save lives immediately."

Liberal MP and foreign affairs critic Marc Garneau also expressed concern the country wouldn't easily be able to leave Iraq once it joins the airstrikes. He questioned what the government will do after the six-month mission ends and if things are going "badly" in the region.

Garneau said while the Liberals are horrified by ISIS, the Conservatives have not made a strong enough case to gain his party’s support.

"We realize how barbaric this group is, and we have to defeat it," Garneau said, noting the party supported the first non-combat mission. "But there's a clear line between combat and non-combat and this government, the prime minister, has not made the case strongly enough for us to support that."

Like the NDP, the Liberals are also calling for Canada to provide increased humanitarian aid to the region.

Meanwhile, Green Party Leader and MP Elizabeth May warned that the airstrikes may be making the situation worse.

"My bottom line is simple: let's not do something that makes things worse," she said of the proposed mission. "(ISIS) is appalling, atrocious, and we must do everything we can to stamp it out. But clearly ISIS wants us to go to war. Why else would they put beheadings on YouTube?"

Last week, ISIS released a fourth video showing the execution of British aid worker Alan Henning. The group, which has seized large parts of Syria and Iraq, is aiming to establish an Islamic state or caliphate in the region.

With a report from CTV's Katie Simpson in Ottawa