Canadian Forces and CF-18 fighter jets engaged in a defensive combat operation against ISIS militants northeast of Mosul during a surprise attack on Kurdish forces yesterday, defence officials said Thursday night.

Speaking at a short-notice technical briefing, Maj.-Gen. Charles Lamarre, director for Canada’s Strategic Joint Staff, told reporters that the militants had been able to carry out an attack on multiple locations near the northern Iraqi city of Mosul — including two locations where Canadian Forces were stationed in their advise-and-assist role.

“It is the largest (attack) that the Canadian Forces training up north have been involved in,” said Lamarre, adding the size of the ISIS contingent was significant. “There was an element of surprise that ISIL brought to this.”

No Canadian Forces personnel were hurt in the fight, but the Kurds did sustain casualties.

Lamarre said the attack marked a departure from ISIS’s usual approach to combat, in that the attacking force was large enough to allow the militants to target multiple locations.

The militants began their assault around 4 pm local time in Iraq and continued throughout the night.

By morning, a counterattack involving Kurdish and Canadian Forces was able to secure the lines ISIS had targeted and push the militants back.

Lamarre said it’s too early to speculate on whether the style of attack marked an emergent trend in ISIS’s tactical abilities — but did note that the militants were using vehicles with plate armour and IEDs they had built themselves, as well as artillery.

News of the operation quickly prompted reaction from politicians online.

Canada CF-18 jets must stay to defeat ISIS. Again, our CF-18s “helped destroy the enemy “and “saved lives” in Kurdish region. I salute #CAF. — James Bezan (@jamesbezan) December 18, 2015

There has still been no rationale put forward by the Canadian Government on why our planes should be removed from the fight against ISIS. — Tony Clement (@TonyclementCPC) December 18, 2015

Critical role for Canada “@davidcommon: Canadian special forces repel #ISIS attack. Lasted 17 hours. Largest event for Canada to date.” — Bob Rae (@BobRae48) December 18, 2015

Prime Minister Justin Trudeau ran on a promise to pull Canadian fighter jets from the mission, arguing that Canada could make a better contribution by focusing its efforts on humanitarian aid and training assistance.

He has repeatedly declined to specify a timeline for when the fighter jets could return home, or to say whether Canada’s surveillance and refuelling aircraft will remain as part of the coalition air force.