The highest-ranking Canadian officer at Norad has demolished a long-held political assumption by telling a parliamentary committee that the U.S. is under no obligation to defend Canada in the event of a ballistic missile attack.

Lt.-Gen. Pierre St-Amand laid out on Thursday — in stark terms — where the military lines of each nation begin and end in the event the North Korean crisis erupts into a shooting war.

"The extent of the U.S. policy is not to defend Canada," said St-Amand, who is the deputy commander of the North American Aerospace Defence Command, which is responsible for defending the skies and maritime approaches to North America. "That's the fact I can bring to the table."

The debate over whether Canada should join the U.S. ballistic missile defence program re-emerged this summer following a series of successful intercontinental missile tests by North Korea, including another missile launch from that country's capital Pyongyang on Friday.

The missile flew over Japan before landing in the northern Pacific Ocean. South Korea's Joint Chiefs of Staff said it travelled about 3,700 kilometres, reaching a maximum height of 770 kilometres.

The Liberal government in its recent defence policy review chose to uphold a 2005 decision by former prime minister Paul Martin to remain outside of the U.S. missile shield.

The often-cited political narrative has been that the U.S. would shoot down a missile if it was headed toward Toronto, Vancouver or Montreal.

St-Amand made clear that is not guaranteed and it would be a decision made "in the heat of the moment" by U.S. political and military leaders.

No direct threat?

The Commons defence committee held a marathon session Thursday about the escalating threat from North Korea, taking in the views of not only military commanders, but also senior diplomatic and intelligence officials, as well as academic experts.

The regime of Kim Jong-un doesn't have Canada in its crosshairs, but the rogue regime does represent a significant threat to global peace, said Mark Gwozdecky, assistant deputy minister for international security at Global Affairs Canada.

He tried to strike an optimistic tone.

"There's been no direct threat to Canada," said Gwozdecky. "In fact, on the contrary, in recent contacts with the North Korean government, including in August when our national security adviser was in Pyongyang, the indications were they perceived Canada as a peaceful and indeed a friendly country."

North Korean leader Kim Jong-un reacts with scientists and technicians of the DPRK Academy of Defence Science after the test launch of the intercontinental ballistic missile Hwasong-14 in this undated photo released by North Korea's Korean Central News Agency. (KCNA/Reuters)

But he said the regime's "actions represent a grave threat to regional security, our friends and allies, South Korea and Japan."

There are signs North Korea is willing to talk if there are no preconditions, Gwozdecky added.

The assistant chief of defence intelligence at National Defence, Stephen Burt, downplayed the notion of a missile attack on North America, calling it a "hypothetical scenario" that could be spun in a number of directions.

"If you go back to the fact the regime in North Korea is primarily motivated by its desire to survive and sustain its rule ... While their rhetoric is colourful and their behaviour occasionally strikes us as peculiar, they're no fools, and they understand the consequences of that kind of an action," Burt said.

A missile is launched during a long and medium-range ballistic rocket launch drill in this undated photo released by North Korea's Korean Central News Agency in Pyongyang. (KCNA/Reuters)

Conservative defence critic James Bezan said he was shocked to hear that North Korea doesn't consider Canada a potential enemy, particularly in light of the country's participation in the Korean War between 1950-53.

He wasn't, however, prepared to say that his party advocates joining ballistic missile defence, saying he will take all of the testimony back to caucus for consideration.

The Conservatives were in favour of joining the U.S. missile shield in 2005 but chose not to follow up during their nine years in power.

Pump up diplomacy

New Democrat MP Randall Garrison said the testimony only reinforces his feeling that there is no military solution to the crisis and that diplomacy is the only way forward.

Experts were divided when they had their chance to testify.

"It's not even clear the Americans want us in missile defence," said Michael Byers, a University of British Columbia defence policy expert, who argued Washington would prefer to see Canada spend more on its conventional defences.

Joining ballistic missile defence would be "purely symbolic," he said, while acknowledging the situation with North Korea is extremely dangerous.