There are more than twice as many foreign fighters in Iraq and Syria compared with 2014, with a big rise in militants coming from Russia, a new report has revealed.
The security intelligence agency the Soufan Group says that there are now between 27,000 and 31,000 foreign fighters from 86 countries who have travelled to the conflict-riven region, up from 12,000 the last time the New York-based group carried out a study, in June 2014.
It said that the international response to the militants was having little effect and that Islamic State (Isis) had managed to energise tens of thousands of people to join it and support it.
The report noted that Russia, with 2,400 fighters, is now believed to be the third-biggest supplier of foreign fighters, with most of them coming from the North Caucasus such as Chechnya and Dagestan. An additional 4,700 came from former Soviet republics, with 5,000 making their way from Europe.
The only countries that supplied more fighters were Saudi Arabia, with 2,500, and Tunisia with its 6,000.
The numbers were compiled from official government estimates, United Nations reports, studies by research
bodies, academic sources, and from other sources quoting government officials.
The report stated that IS (Daesh) is likely to survive in some form for a considerable time to come and will attract more recruits from abroad. "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.
"Even if the Islamic State is a failing enterprise in steady decline, it will be able to influence the actions of its adherents, and it may become more dangerous as it dies. The challenge to the international community remains, and will be harder to meet as foreign fighters become more adept at disguising their movements and more uncertain in their future intentions," the report said.
The group said that up to a third of foreign fighters returned to their home countries, which posed problems for domestic security agencies.
Senior vice president of the Soufan Group, Richard Barrett told IBTimes UK that governments are better at estimating numbers of their citizens joining Isis. He added that whether this would continue to grow is down to two main factors.
"The first is border controls and border controls are beginning to get tighter; it is harder to get through Turkey. The second is: what happens to Islamic State if it starts to look like it is collapsing? If the stories of its brutality trump the stories of its state building then I think it will lose its appeal," Mr Barrett said.
A report by the Global Terrorism Index last month found that there could be up to 42 groups affiliated with Isis, but Mr Barrett pointed out that this does not mean there is a lack of unity among them.
"The great majority join ISIS. That is the flag that everybody recognizes, that is the group that has the big appeal and the other groups are more nationalist in their objectives," he said.