The terrorist group behind the growing insurgency in Iraq claims it is expanding its network of foreign fighters due in part to a substantial online presence that attracts young sympathizers overseas.

Of the 6,000 Islamic State in Iraq and al-Sham (ISIS) fighters in Iraq, half are believed to be foreigners. The well-organized terrorist group uses slick recruitment videos in an effort to recruit would-be western militants.

In one video released by the group, the words “there is no life without Jihad” float out at the viewer in English before several armed men explain why others like them should join the struggle.

Twenty-year-old Ryad Khan from Wales is one of hundreds of Britons who left their homes to join ISIS. One-time straight-A student appears in one of the recruitment videos clutching an assault rifle and asking potential recruits, “What prevents you from attaining martyrdom?”

Back in Britain, Khan's mother says she is devastated by his rapid transformation. She believes her son was brainwashed by extremists.

“Please send my son back to me before I die,” she says. “Or it’s going to be too late for Ryad and he’s going to regret this for the rest of his life.”

ISIS says their fighters come from Bangladesh, Cambodia, and Australia. Canada can also be added to his list. About 30 Canadians have joined the Jihad in Iraq and Syria, leaving the country to fight with ISIS.

Last week, CTV News confirmed that Calgary man Farah Mohamed Shirdon is among those fighting with the terrorist cell. He appeared in a recent video released by ISIS, in which he uttered threats directed at Canada and U.S. oppressors. In the video, he is also seen burning his Canadian passport.

Experts say the men are first preyed upon by radical preachers who glorify terrorism and violence.

“They poison their minds, and they tell the young men that you can’t live harmoniously in this country religiously, you have to live in a pure Islamic state,” says Dr. Usama Hasan, of the London-based counter-extremism think-tank, Quilliam Foundation.

At a rally held in Calgary on Saturday, dozens demonstrated against terrorism, and warned Ottawa that radicalization happens within Canada’s borders.

Riyaz Khawaja, a member of the Hussaini Association of Calgary, says he wants to know how young men in his community are becoming convinced to fight for these causes.

“The Canadian government, CSIS intelligence agencies, should really take this serious note, and keep an eye on the radicals, where they're getting this information from," Khawaja told CTV News.

His group’s website takes a hardline stance against extremists, strongly condemning “the cowardice and heinous act of terrorism around the globe against humanity.”

Canadian security officials and police across the country say they’re watching these groups closely. But they admit it’s difficult to catch everything when net-savvy young men can access extremism anywhere online.

With a report from CTV News’ Richard Madan