OTTAWA -- Liberal Leader Justin Trudeau poked fun at the government's desire to help fight ISIS, telling a friendly audience Thursday it's "not about whipping out our CF-18s to show how big they are."

Speaking at an event hosted by progressive think-tank Canada 2020, Trudeau repeated the same message he's delivered all week on Iraq: the government hasn't made the case for war.

"(Harper's) made no effort to make a non-partisan case for war; he dares us to oppose it," Trudeau said.

After giving a keynote address, Trudeau sat for a "fireside chat" with veteran journalist Don Newman.

During the interview, Trudeau made what was likely intended to be a joke about the CF-18 fighter jets, which the government reportedly wants to send to Iraq to fight ISIS.

The "whipping out" comment was met with uncomfortable laughter.

Jobs Minister Jason Kenney tweeted his disapproval.

"Remarkable that Justin Trudeau uses juvenile humour ("whip it out") to describe the use of force in combating genocide," Kenney wrote. "Is this how Prime Minister Justin Trudeau would conduct himself in discussing use of air power at a NATO summit?"

NDP Leader Tom Mulcair called Trudeau's comments "childish."

Remarkable that Justin Trudeau uses juvenile humour ("whip it out") to describe use of force in combatting genocide: http://t.co/ulZae4fBBq — Jason Kenney ن (@kenneyjason) October 2, 2014

He also repeated his line that the government has yet to "come clean" with Canadians about its military plans.

During question period, NDP foreign affairs critic Paul Dewar called on the government to send investigators to assist in the "investigation and prosecution" of ISIS sex crimes and other human rights abuses.

Neither Dewar nor anyone else in the NDP explained how sending lawyers or investigators to stop rape would work, particularly given the party's apparent opposition to sending ground forces to the large area within Syria and Iraq where ISIS claims to have established an Islamic state.

Kenney returned to Twitter because Dewar's comments left him baffled.

"Wow," he wrote. "Apparently the NDP thinks that (ISIS's) mass rape can be stopped by seminars on gender violence and firmly worded resolutions."

Kenny added: "France, U.K., Germany, Italy, Denmark, Netherlands, Sweden et al., but not our NDP, which apparently opposes the responsibility to protect."

Wow. Apparently the NDP thinks that #ISIL's mass rape can be stopped by seminars on gender violence and firmly worded resolutions. — Jason Kenney ن (@kenneyjason) October 2, 2014

Dewar fired back with a tweet of his own: "no need to be glib. I asked for targeted aid to victims of sexual violence a month ago. Baird committed action. Where is it?"

The government is expected to announce plans for an expanded military role Friday.

Harper has said Canada will respond to requests from U.S. President Barack Obama as well as the Iraqi government for additional help from the international community.

Earlier Thursday, the UN accused ISIS of committing war crimes -- mass murders, beheadings and sexual violence -- and suggested the group should somehow be held accountable by international courts.

"The array of violations and abuses perpetrated by (ISIS) and associated armed groups is staggering, and many of their acts may amount to war crimes or crimes against humanity," UN commissioner for human rights Zeid Ra'ad al Hussein said Thursday.