Ottawa (AFP) - Canadian special forces have twice exchanged gunfire with Islamic State fighters in Iraq since the first confirmed ground battle between Western troops and IS earlier this month, a senior officer said Monday.

Recalling the first incident, Captain Paul Forget told a briefing: "Two similar events have occurred over the last week and, in both cases, Canadian special operations forces, again acting in self-defense, effectively returned fire, neutralizing the threat."

No Canadians were injured, he added.

The first clash mid-January in which the Canadians came under mortar and machine gun fire while training Iraqi troops near front lines underscored political divisions in Ottawa over the US-led mission against IS.

Canada's opposition leader accused Prime Minister Stephen Harper of having lied when he promised no ground combat alongside coalition airstrikes against the Islamic State group.

An unapologetic Harper said Canadian troops were responding to an evolving threat.

"We want to advise and assist Iraqi forces, particularly the Kurdish forces, to lead the combat themselves," Harper said at a news conference on Thursday.

"But let me be clear, this is a robust mission. We are there to make those guys effective so they can take on the Islamic State and deal with them. If those guys (IS) fire at us, we are going to fire back and we are going to kill them."

Canada sent 69 special forces to train Iraqis, and some 600 air crew and other military personnel -- as well as six fighter jets and other military aircraft -- to the region in November to participate in air strikes.

The special forces have also designated targets for coalition aircraft.

The opposition has decried what they referred to as mission creep -- incremental changes to mission parameters outlined to parliament in September -- but Forget said it is a normal "evolution of our advise and assist capacity."