U.S. intelligence officials said on Wednesday that more than 150 American citizens have either traveled to Syria or attempted to do so, primarily to join the Islamic State (IS) terrorist group.
Nick Rasmussen, director of the National Counterterrorism Center, told members of the House Homeland Security Committee that an "unprecedented" number of foreign fighters had traveled to Syria to battle Syrian President Bashar al-Assad and other rebel groups in the country’s civil war. More than 20,000 fighters from 90 different countries have entered the conflict, including 3,400 militants from Western countries and more than 150 U.S. persons.
Once in Syria, Western fighters can receive training and could then eventually return to countries in Europe and the United States to conduct terror attacks.
"The battlefields in Iraq and Syria provide foreign fighters with combat experience, weapons and explosives training, and access to terrorist networks that may be planning attacks which target the West," Rasmussen said. "This shared threat has prompted even closer cooperation across U.S. federal agencies and with our international partners, particularly in Europe."
Many fighters enter Syria by crossing the country’s porous northern border with Turkey, which has visa-free travel agreements with more than 69 countries and has become a transit point for militants. The Turkish government has attempted to reduce the flow of foreign fighters into Syria in recent months by compiling a list of thousands of individuals banned from entry into Turkey.
Francis Taylor, under secretary for intelligence and analysis at the Department of Homeland Security (DHS), said that while there is not "any specific, credible, imminent threat to the [U.S.] homeland," intelligence officials have become concerned that "Syria could emerge as a base of operations for al Qaeda’s international agenda, which could include attacks against the homeland."
Domestic attacks by individuals radicalized in the United States also remain a concern for intelligence officials.
Michael Steinbach, assistant director of the counterterrorism division at the Federal Bureau of Investigation (FBI), noted that IS effectively uses social media to "propagate its extremist ideas."
"In January 2015, [IS] released a video via social media networking sites reiterating the group’s encouragement of lone offender attacks in Western countries; specifically advocating for attacks against soldiers, patrons, law enforcement and intelligence members," he said. "Several incidents have occurred in the United States and Europe over the last few months that indicate this ‘call to arms’ has resonated among [IS] supporters and sympathizers."
Additionally, al Qaeda in the Arabian Peninsula (AQAP) released in December the latest edition of its online English-language magazine Inspire, which urges followers abroad to plan attacks and includes instructions for building a bomb.
The FBI is working with DHS and local law enforcement agencies to share information and combat the process of radicalization, Steinbach said.
Rasmussen said the threat of attacks from homegrown terrorists "will remain at its current level" with "fewer than 10 uncoordinated and unsophisticated plots annually from a pool of up to a few hundred individuals, most of whom are known to the [intelligence community] and law enforcement."
Rep. Michael McCaul (R., Texas), committee chairman, expressed concerns in his opening statement about the continuing growth of foreign fighters in Iraq and Syria despite U.S. airstrikes. U.S. agencies also need to devote more resources to countering the propaganda of terrorist groups at home, he said.
"I am worried about our ability to combat this threat abroad, but also here at home," he said. "I wrote to the president recently and raised concerns that we still have no lead agency in charge of countering domestic radicalization and no line item for it in the budgets of key departments and agencies. I am also concerned that the few programs we do have in place are far too small to confront a threat that has grown so quickly."