WASHINGTON, Sept. 27 (UPI) -- FBI Director James Comey told U.S. Senators on Tuesday that intelligence and law enforcement agencies are concerned a "terrorist diaspora" will occur globally in a few years after the Islamic State loses control.
"The so-called caliphate will be crushed," he said, referring to the militant group also identified as Daesh, ISIS and ISIL. "The challenge will be: Through the fingers of that crush are going to come hundreds of very, very dangerous people. They will not all die on the battlefield in Syria and Iraq. There will be a terrorist diaspora sometime in the next two to five years like we've never seen before."
He warned that nations must be ready.
"We must prepare ourselves and our allies particularly in western Europe to confront that threat because when ISIL is reduced to an insurgency and those killers flow out they will try to come to western Europe and try to come here to kill innocent people."
He noted fighting terrorism is the FBI's No. 1 priority but the "the terrorist threat against the United States remains persistent and acute."
"As the threat to harm Western interests evolves, we must adapt and confront the challenges, relying heavily on the strength of our federal, state, local and international partnerships," he said. "Our successes depend on interagency cooperation; among those partners are with me today; the Department of Homeland Security and the National Counterterrorism Center to address current and emerging threats."
Comey mentioned cyber threats are sometimes linked to terrorism.
"Virtually every national security threat and crime problem the FBI faces is cyber-based or facilitated," he said. "We face sophisticated cyber threats from state-sponsored hackers, hackers for hire, organized cyber syndicates and terrorists. "
He noted the FBI is on the lookout for terrorists in the United States and "are confronting an explosion of terrorist propaganda and training available via the Internet and social networking media."
"We continue to identify individuals who seek to join the ranks of foreign fighters traveling in support of ISIL, and also homegrown violent extremists who may aspire to attack the United States from within," he said.
Committee Chairman Sen. Ron Johnson, R-Wis., noted the diaspora has already begun.
"We haven't reduced their capability," Johnson said. "We're poking the hive. We've done some damage to it but the killer bees are leaving the hive. They're setting up new hives."
National Counterterrorism Center Director Nicholas Rasmussen also testified, saying intelligence officials had long predicted the threat would develop as the Islamic State's power was decreased.
"It's not surprising. It puts us in a period of sustained vulnerability that I don't think any of us are comfortable with. But I think it's a reality," he said.
Some senators said FBI has missed opportunities to head off home-grown terrorist attacks, including the shooting at the Orlando, Fla., nightclub Pulse in June when 49 people were killed and bombings earlier this month in New York and New Jersey.
"I'm also troubled the FBI is not even willing to admit they made some mistakes," Sen. Rand Paul, R-Ky., said. "These are judgment calls and the judgment calls were incorrect, and I think we should just admit that and look at some of the facts."
Paul said the FBI should have continued its investigation of the Orlando shooter, Omar Mateen, prior to the shooting because the agency might have learned about his plan to attack the club.
"We should keep [investigations] open longer ... as long as the facts warrant," the FBI director said. "We have the policies and the tools we need to do this well." He added that agents have to make a "judgement every day" about whether specific cases merit more investigation.
Comey said the FBI is continuing to review how it handled the Florida case and it will assess inquiries into New York and New Jersey bombing suspect Ahmad Rahami.
Homeland Security Secretary Jeh Johnson said threats have moved from terrorist-directed attacks "to a world that also includes the threat of terrorist-inspired attacks."