Canada will expand its military mission against Islamic State (Isis) by launching air strikes against its positions in Syria as well as Iraq, Prime Minister Stephen Harper said on 24 March.

That will make Canada the second Nato member nation after the United States to attack Islamic State positions in Syria, which have also been hit by jets from Jordan and the United Arab Emirates.

Harper also said Canada plans to extend its six-month mission by a year to the end of March 2016. Canada now has around 70 special forces troops operating in northern Iraq and six Canadian jets are taking part in US-led bombing missions against IS in Iraq.

Harper, facing a tough challenge to retain power in October's general election, portrays rival political parties as weak on terror and says only his Conservatives properly understand the threat posed by IS.

Harper told legislators that Canada must strike at the Syrian power base of IS.

"Isil's fighters and much of its heavier equipment are moving freely across the Iraqi border into Syria, in part for better protection against our air strikes. In our view, Isil must cease to have any safe haven in Syria," he said.

Extending the mission to Syria is politically divisive, since critics say this means bombing strikes will need the approval of Syrian President Bashar al-Assad.

Harper said Canada would not seek the consent of the Syrian government to launch the attacks.

The left-leaning New Democrats – the main opposition party – say they will vote against expansion of the mission on the grounds that Canada is gradually being dragged into a war not of its own making.

Harper also told parliamentarians that Canada and others "must avoid, if we can, taking on ground combat responsibilities" in Iraq, saying that was the job of the Iraqi military.

The centrist Liberals, who polls show have a chance of winning power in October, have yet to make their position clear.