The deadly attacks in Paris serve as a vivid reminder that jihadists are at war with those they disagree with, and the world must confront them, Canadian Prime Minister Stephen Harper said on Thursday.

"The international jihadist movement has declared war. They have declared war on anybody who does not think and act exactly as they wish they'd think and act," Harper told reporters when asked about Wednesday's attack.

"We may not like this and wish it would go away, but it's not going to go away, and the reality is we are going to have to confront it."

Harper spoke as a manhunt was underway in France for two brothers suspected of being the Islamist gunmen who killed 12 people in Wednesday's attack on a satirical weekly newspaper in Paris.

Harper said any doubts in Canada about the reality of threats posed by such extremists should have vanished on Oct. 22. That was the day when a radicalized Canadian gunman killed a soldier at the national war memorial and then stormed the Parliament building.

The Ottawa attack underscored fears that Canada, a close ally of the United States in its campaign against the Islamic State militant group, had been targeted in a reprisal.

Other manifestations of the threat posed by militant Islam in Canada included the case of the so-called "Toronto 18," Harper said, referring to the 2006 arrests of a group of men charged with planning attacks on Toronto-area targets in a plot to get Canada to withdraw troops from Afghanistan.

Canada's security agencies have been able to prevent most attacks by extremists from coming to fruition, Harper said.

"But the fact of the matter is this recent development, the emergence of the so-called Islamic State, its sudden control of a vast territory with vast amounts of financial resources, has escalated this to a whole new global level," he added.