The Associated Press has reported foreign fighters are traveling to Syria and Iraq in droves to join ISIS and other terrorist groups.
U.S. Intelligence officials said about 20,00 people from around the world, including 3,400 people from Western nations, have left their homes to join terrorist groups.
According to testimony obtained by the Associated Press, officials told the House Homeland Security Committee that as many as 150 Americans have tried to reach the war zone in Syria, and some have succeeded.
Nick Rasmussen, chief of the National Counterterrorism Center, said that the number of people joining the fight from around the globe was unprecedented. Officials fear that fighters may return home to the U.S. and Europe to commit acts of terror.
Officials have acknowledged it’s difficult to track how many people have gone to fight for ISIS in Syria in Iraq because the CIA doesn’t have a permanent presence in Syria.
"Once in Syria, it is very difficult to discern what happens there,” Michael Steinbach, the FBI's assistant director for counterterrorism, said in prepared testimony on Wednesday. "This lack of clarity remains troubling.”
Today, the Wall Street Journal reported President Obama would seek Congress’ approval to start more aggressive military operations against ISIS. Recently, the U.S. has helped lead an extensive bombing campaign against ISIS.