FBI warns about 'terrorist diaspora' after IS defeat

Senior US national security officials on Thursday warned about a possible rise in extremist violence with the spread of a "terrorist diaspora" once the Islamic State group in Iraq and Syria is defeated.

"We all know there will be a terrorist diaspora out of the caliphate as military forces crush the caliphate," FBI Director James Comey told a hearing of the House Homeland Security Committee, referring to the Islamic state proclaimed by the jihadist group.

Thousands of fighters will spread worldwide "and our job is to spot them and stop them before they come to the United States to harm innocent people," he added.

FBI Director James Comey listens during a hearing of the House Homeland Security Committee on July 14, 2016 in Washington, DC ©Brendan Smialowski (AFP)

The IS group's defeat in Iraq and Syria will make it "desperate to demonstrate its continued vitality, and that is likely to take the form of more asymmetric attacks, of more efforts at terrorism," Comey said.

CIA director John Brennan estimated last month that some 18,000 to 22,000 IS fighters remained in Iraq and Syria, and he predicted they would probably intensify attacks around the world even as they come under pressure in Iraq and Syria.

The jihadi group has ceded an increasing amount of territory in recent weeks, especially in Iraq, where it lost control over the Sunni city of Fallujah and a major air base in Qayyarah, some 40 miles (60 kilometers) from the city of Mosul, the IS group's de facto capital in Iraq.

However, that has not stopped the jihadists from staging deadly attacks in Baghdad and elsewhere.

Although the Islamic State group's grip in Iraq and Syria is weakening, there may be a significant lag between the US-led coalition's battlefield victories and reducing the IS group's capability to stage attacks, Nicholas Rasmussen, director of the National Counterterrorism Center, told the committee.