A masked man speaking in what is believed to be a North American accent in a video that ISIS released in September 2014 is pictured in this still frame from video obtained by Reuters October 7, 2014.

The number of foreign fighters in Iraq and Syria has more than doubled since last year to at least 27,000, a report by an intelligence consultancy said on Tuesday, highlighting the global dimension of the conflict.

The figures, compiled by The Soufan Group, indicate that efforts by countries around the world to stem the flow of foreign fighters to Iraq and Syria and blunt the appeal of violent organizations such as ISIS appear to have made little impact.

“The foreign fighter phenomenon in Iraq and Syria is truly global,” the New York-based organization’s report said.

“The Islamic State has seen success beyond the dreams of other terrorist groups that now appear conventional and even old-fashioned, such as Al-Qaeda.

“It has energized tens of thousands of people to join it, and inspired many more to support it.”

In all, between 27,000 and 31,000 foreign fighters from 86 countries have travelled to Iraq and Syria, the Soufan Group said, compared to a figure of around 12,000 foreign fighters in Syria when it last published a similar study in June 2014.

The largest number travelled to the two countries, across which ISIS controls a swathe of territory, from the Middle East and the Maghreb, with around 8,000 foreign fighters each.

Around 5,000 made their way from Europe, with a further 4,700 from former Soviet republics.

The Soufan Group added that between 20 and 30 percent of foreign fighters were returning to their home countries, creating major challenges for domestic security agencies as ISIS in particular looks to carry out an increasing number of attacks overseas.

The group claimed responsibility for a massive attack in Paris last month that left 130 dead, and its fighters have been held responsible for violence in a litany of countries ranging from Iraq to Bangladesh.

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