Security experts are warning of a new wave of violence by so-called "lone wolf" radicals, impressionable individuals who fall prey to extremist ideology and choose to act on them.

It’s proving difficult to police these “self-radicals,” who may be inspired by militant organizations that, via social media and online postings, encourage others to kill and terrorize in their home countries.

“The number of individuals that our intelligence agencies are attempting to monitor are again getting longer and longer,” security expert John Thompson told CTV News.

As Canada reels from two separate incidents that left two soldiers dead in one week, investigators now say they believe the tragedies were caused by individuals who held radical views and may have acted on them alone.

On Oct. 20, Martin Couture Rouleau appeared to be acting alone when he struck two soldiers with his car in a Quebec town, killing Warrant Officer Patrice Vincent in what is believed to be a targeted attack.

Two days later, Michael Zehaf-Bibeau shot dead Cpl. Nathan Cirillo at the National War Memorial in Ottawa, and then stormed Parliament’s Centre Block. Authorities later said they believed Zehaf-Bibeau was also acting alone.

This form of terrorism is a departure from coordinated Sept. 11-style attacks, but it’s still a growing threat, security experts say.

“I would say the most likely type of attack is one of these homegrown, violent extremists or lone offenders,” said Matthew Olsen, former director of the U.S. National Counterterrorism Center.

As investigators link some of the offenders to ideals held by extremist organizations such as the Islamic State, mainstream Muslim groups in Canada say they are working with police to counteract this type of behaviour.

“It’s not just their civic duty but it’s also their religious duty to report that to the authorities,” Ishaan Gardee, of the National Council of Canadian Muslims, told CTV News.

But stopping the acts before they happen is a long shot.

Unlike in Europe, North American authorities err on the side of freedom and civil liberties over security.

“Unless they can show up in front of a judge and say, ‘A terrorist act is going to be committed unless you do this,’ and they can provide evidence to that effect, I think there’s a concern that the judge is going to send them packing,” said Christian Leuprecht, a security expert with the Royal Military College of Canada.

With a report by CTV’s Peter Akman