An assessment of foreign fighters in Syria and Iraq conducted by strategic security intelligence consultants highlights the increasing problem of jihadists leaving the European Union (EU) to fight in the Middle East.

The work on foreign fighters, published in a report from the Soufan Group, reveals that in June 2014 the group identified approximately 12,000 foreign fighters from 81 countries, but just 18 months later the number has more than doubled with between 27,000 and 31,000 people now having traveled to Syria and Iraq from at least 86 countries.

Although the report finds volunteer numbers from North America remain relatively flat, it states that the number of foreign fighters from Western Europe has more than doubled since the previous report.

The most recent figures available indicate more than 5,000 foreign fighters from member states of the EU have gone to Syria. Although every western European country that has published its figures shows an increase in people traveling to Syria, certain nations feature disproportionately.

The report states that French authorities indicate around 1,800 individuals left France to fight as of October 2015. As of November 2015 an estimated 760 foreign fighters left the UK, and a further 760 from Germany, along with 470 from Belgium (as of October 2015).

In other words, of the 5,000 or so foreign fighters from Western Europe that have been identified, almost 3,700 of them come from just four EU nations. This presents what the report describes as “a significant challenge to security and law enforcement agencies.”

According to the report:

Although anecdotal evidence suggests that it has become harder for individuals to leave territory controlled by the Islamic State, as time has passed, the number of individuals returning to their home countries from the fighting in Syria and Iraq has increased.

The problem for EU nations is that although some will be leaving because, in the report’s words, they “have had enough of the violence” and “some may have become disillusioned with the Islamic State and its leadership,” others may taken the decision “to pursue their goals elsewhere.”

The report warns that November’s Paris attacks “may reflect a growing trend of overseas terrorism being planned and organized from the Islamic State.”

Methods of recruitment for future foreign fighters sought by Islamic State is also analysed in the report. It finds “more evidence of community-based recruitment in countries with the highest numbers of foreign fighters, where groups of acquaintances are

drawn into a common identity.” An example cited is the Molenbeek district of Brussels, where several of the terrorists who planned and carried out the Paris attacks lived and knew each other.

A further reason for alarm regarding the growing number of foreign fighters is that they become recruiters themselves. As the report explains, “over time, people who have already gone to Syria reach out in person to their friends and acquaintances to encourage them to do the same.”

The report’s conclusion is chilling:

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.