The rise of ISIL has brought with it several challenging dynamics for counter-terrorism," the report said. "The flow of foreign fighters into Iraq and Syria since 2011 is the largest influx in modern times. "Current estimates now range from 25,000 to 30,000 fighters, from roughly 100 countries." The report also warns that the flow of foreign fighters does not appear to be diminishing, with more than 7000 arriving in the first six months of 2015.