Citing sources, CBC said the three Canadians interrogated the US journalists to obtain computer passwords and PINs. The captors stole from the journalists’ banking accounts and wrote cruel letters to family members pretending to be the hostages.

They also used credit cards to buy electronic equipment on eBay.

Curtis and Schrier were held in captivity between 2011 and 2013. Schrier escaped from his kidnappers last year, while Curtis was released by the jihadist Al-Nusra Front group last month.

Peter Theo Curtis, who was released on Sunday from two years in the captivity of insurgents in Syria,

talks to reporters near his mother's home in Cambridge, Massachusetts August 27, 2014. (Reuters / Brian Snyder)

The Canadian government earlier estimated that around 130 Canadians have joined extremists groups overseas. However, CBC now believes that numbers is somewhere between 200 and 300 people.

Out of various extremists groups, most of the individuals are joining the Islamic State (IS), previously known as Islamic State of Iraq and Syria (ISIS or ISIL).

Spread of ISIS

The IS is now in control of the territory the size of UK, a senior US counter-terrorism official Matthew Olsen, said on Wednesday, adding that the group sees itself “as the new leader of the global jihadist movement.”

The extremist group is also making US$1 million a day from selling oil and from hostage ransoms, as well as having 10,000 militants in its ranks.

Olsen added that the IS was able to expand rapidly due to weak governments in Syria and Iraq.

“[IS] threatens to outpace Al-Qaeda as the dominant voice of influence in the global extremist movement,” he said.

The Islamic State began attracting worldwide attention this summer as it made rapid territorial gains in western and northern Iraq, threatening religious and ethnic minorities with death unless they converted to their extreme brand of Islam. Their success triggered renewed military action by the US in the form of airstrikes and the deployment of military advisors. On Tuesday, President Barack Obama announced 350 additional troops would be sent to Iraq to bolster diplomatic security.