The increased flow of foreign fighters into Syria is raising fears that the war torn country is becoming a haven for Islamist militants. The U.S. Central Intelligence Agency’s second in command, Michael Morrell, recently said that the combination of extremism and civil war in Syria now poses the greatest risk to U.S. national security. Counterterrorism officials say that jihadist militants are streaming into Syria at greater rates than they did into Iraq at the height of the insurgency.

Many militants belong to the extremist Nusra Front, but new groups are forming under the more extremist umbrella group, the Islamic State of Iraq and Syria. The head of the opposition Free Syrian Army (FSA), General Salim Idris, recently accused Islamist groups of receiving funding from the Assad regime, and there have been increasing clashes between FSA forces and jihadist groups over arms and supplies. Meanwhile, the head of the opposition Syrian National Coalition, Ahmed al-Jarba, said he is working with the FSA to pull together all rebel groups into one unified army.