The FBI claims that extremist groups with ties to al-Qaeda in Syria are attempting to recruit Americans and get them to carry out attacks when they return to America, and officials say that at least 70 Americans have traveled to Syria since civil war broke out in the country.

According to The New York Times, "tracking Americans who have returned from Syria had become one of the bureau’s highest counterterrorism priorities." The bureau's director, James Comey, told reporters, "We are focused on trying to figure out what our people are up to, who should be spoken to, who should be followed, who should be charged." Specific numbers were not provided.

Tracking migration to and from Syria has become a complex problem for western countries in recent years. Analysts estimate that at least 1,200 European Muslims have traveled to Syria as well.

Last year, Eric Harroun, a former U.S. soldier ho documented his combat activity online, was charged for fighting with the al-Nusrah Front, which has links to al-Qaeda. Harroun is white, although in a Foreign Policy article published last year, his religious affiliation was unclear. In September, he plead guilty, the Times writes, to charges "involving conspiracy to transfer defense articles and services."