Earlier this summer, the terrorist group Islamic State in Iraq and the Levant (ISIL) released a chilling recruitment video calling on young people in the West to leave their families and come to the Middle East to train for what it calls holy war. It featured a Canadian who had embraced a violent ideology, travelled to Syria, and was killed there in a firefight last year.

More recently, ISIL produced a disturbing photograph of a seven-year-old boy holding aloft the severed head of an enemy fighter. The boy, an Australian citizen, had been taken to the Syrian battlefield by his father. Such is the nature of ISIL and other like-minded groups, which is why the Canadian Security Intelligence Service and other Western security agencies are paying close attention to calls to join terrorist movements – calls that are finding audiences in our own countries.

Like other propaganda efforts, the ISIL video tried to romanticize the transformation of someone into a religious warrior. Fortunately, most people will understand that there is nothing romantic about killing and dying for such a cause. CSIS liaises with many cultural communities, and I can say without doubt that the extremist narrative of the West being at war with Islam is rejected by the vast majority of Muslims in Canada.

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Yet violent ideologies still have traction in certain quarters. Hundreds and hundreds of mostly young people – from North America, from Australia, from the United Kingdom, from all over Europe and across the Middle East – are signing on with ISIL, al-Qaeda, al-Shabaab or any number of fanatical groups that commit unspeakable violence in a global war against pluralism, democracy, human rights and gender equality. It is now public knowledge that well over 100 Canadians have left Canada to support or train with terrorist movements abroad. Most are men, but some are women. Some are immigrants to Canada, and some are Canadian-born.

Some of these individuals have been killed in the conflict theatres to which they have travelled, such as the two young men from London, Ont., who died attacking a gas facility in Algeria, and a number of other young men from Calgary who met a violent end in Syria or Iraq. One Canadian reportedly killed in Syria had been convicted for his role in the "Toronto 18" terrorist plot of 2006, demonstrating the tenacious nature of this extremist ideology.

The most obvious national-security threat is the one posed by extremists who return. How many are coming back to Canada more radicalized than when they departed? Will their status as veterans of a foreign conflict better enable them to recruit other Canadians? Will they use their foreign contacts to set up networks in Canada to facilitate the movement of fighters, materiel and money in and out of the country?

And, most importantly, will they use their terrorist training to attempt violent acts here in Canada? This is a very real prospect. Europe has already suffered such an attack, where a French citizen and "returnee" from Syria went on a shooting spree in Belgium and killed a number of innocent civilians.

Even if a Canadian extremist does not immediately return, he or she is still a Canadian problem. No country can become an unwitting exporter of terrorism without suffering damage to its international image and relations. Just as Canada expects other nations to prevent their citizens from harming Canadians and Canadian interests, we too are obligated to deny Canadian extremists the ability to kill and terrorize people of other countries.

The movements and travel of highly radicalized individuals pose a tremendous challenge. The Combating Terrorism Act passed in 2013 is a vital and welcome instrument when law enforcement has clear evidence of someone travelling for terrorist purposes, but the plans and intentions of such people are generally not obvious or publicized and thus tools to detect such travel are increasingly important.

Of course, the international character of terrorism also requires international collaboration, as no single country or security agency can manage the problem alone. Investigating and tracking extremists and terrorists abroad, sometimes in failing states and in extremely hostile and chaotic environments, requires making full use of Canada's long-standing trusted relationships with intelligence partners around the world. In an interconnected world of high personal mobility and globalized communications, these relationships are more necessary than ever before.

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Ultimately, national security is a shared exercise, led by the government and involving the whole of the intelligence and law enforcement sector. But perhaps our most important partner is the Canadian public, on whose co-operation we in the security community depend. Parents or community leaders who are worried that someone is being radicalized toward violence, or planning to travel for terrorist purposes, can be vitally important contributors to our collective effort. The significant number of terrorist-related arrests in recent years – from the Toronto 18 plot, which culminated in numerous convictions, to several major cases now before the courts – provides unmistakeable evidence that Canadians must never assume that mass-casualty terrorism cannot happen here.

In working to fulfill our mandate, CSIS ensures that our activities to keep Canada safe will always be consistent with Canadian values and Canadian law. The changing threat environment and difficult challenges such as terrorism-related travel do not change our commitment to those first principles.

For 30 years we have dedicated ourselves to protecting Canada's security interests, and Canadians can be assured their safety remains our highest priority.

Michel Coulombe is director of the Canadian Security Intelligence Service.