The Soufan Group, an international consultancy firm based in New York, used UN data, figures from official government estimates, and academic resources to come up with their findings. In June 2014, 12,000 foreign fighters in the region were identified, and now, there are 27,000 to 31,000 from 86 different countries. Tunisia has the largest number of recruits, about 6,000, followed by Saudi Arabia with 2,500; Russia with 2,400; Turkey with 2,100; and Jordan with 2,000, Newsweek reports. About 120 fighters left the U.S. to fight in Syria and Iraq, the report says, and 40 have returned.

The number of recruits from Russia and Central Asia are up nearly 300 percent, and the number of fighters from Western Europe has more than doubled.