NDP Leader Tom Mulcair is foregoing the celebration and raising red flags following reports that a Canadian sniper in Iraq shattered the world record for the longest confirmed kill.

In a letter Friday to Prime Minister Justin Trudeau, Mulcair said the incident "seriously calls into question your government's claim that Canadian forces are not involved in direct combat in Iraq."

National Defence says the sniper is part of the Joint Task Force 2 special forces unit and was supporting Iraqi forces in their fight against the ISIS when he shot an enemy fighter from 3,540 metres away.

That is more than a kilometre farther than the previous record, held by a British sniper who shot a Taliban fighter in Afghanistan in 2009.

Officials have refused to provide any other details about the incident, including where and when it occurred, citing operational security. But they maintain that the soldier was operating within the established limits of Canada's so-called "advise and assist" mission in Iraq.

Those limits, however, have been repeatedly questioned over the course of the nearly four-year mission, with much of the debate revolving around whether Canadian soldiers are engaged in combat.

Questions over role

While news of the shot has spread like wildfire, prompting accolades and even disbelief from current and former military personnel around the world, Mulcair demanded Trudeau provide answers about the mission in Iraq.

"Will you now confirm that Canadian troops have engaged in ground combat since your government took office?" he wrote.

"Why have you not declared that the current military operation is now a combat mission? Why has there been no debate in the House of Commons regarding this change of mission?"

Opposition parties have repeatedly accused the Liberals of misleading the public about the nature of Canada's mission in Iraq by claiming that Canadian troops are not in combat.

That includes revelations three years ago that Canadian troops were calling in airstrikes on ISIS targets, and last November when it was revealed they could shoot in situations other than self-defence.

But National Defence spokesman Daniel Le Bouthillier stood by past assertions Friday that Canadian soldiers are not engaged in combat in Iraq, despite the record-breaking shot.

"Members of the Canadian Special Operations Task Force do not accompany leading combat elements, but enable the Iraqi security forces who are in a tough combat mission," he said.

"This takes the form of advice in planning for their operations and assistance to defeat (ISIS) through the use of coalition resources."

The latest controversy comes as the clock ticks down on the current mission in Iraq, whose mandate is set to expire next week.

The Liberals have said Canada will maintain a presence in Iraq and the fight against ISIS, though officials say no decision has been made on whether to extend the current mission or change it.

Canada has about 200 special forces operating in northern Iraq, including inside Mosul, supported by a combat hospital, a helicopter detachment, a military surveillance plane and an air-to-air refuelling aircraft.