FBI Director James Comey repeated his concerns Thursday over a "terrorist diaspora" that he believes will occur once ISIS territory in Iraq and Syria is "crushed" by coalition forces.

Comey said during a speech at a national security summit at the University of Texas at Austin that he expects these individuals to flow outward largely to Western Europe, Southeast Asia, and North Africa.

Labeling the impending phenomenon the "ghost of Christmas future," Comey used his remarks to urge government leaders and intelligence officials in Western Europe to "break down the barriers" in the EU and share intelligence and critical information in an effort to crack down on the terrorism threat. He did not make any references to Wednesday's attack in London.

Comey compared Europe's need to unite on security issues to changes in the U.S. following the 9/11 attacks. He described Western Europe as FBI's front lines in preventing those individuals from committing violence outside of the so-called caliphate.

In speaking to trend shifts the FBI has seen domestically with ISIS followers, Comey said that the foreign traveler issue that peaked during the summer of 2015 "hit the floor" in 2016 and has since stayed there. While ISIS's capacity to direct people to travel to the caliphate has dropped, the FBI chief called the ability of terrorists to use social media and the internet to inspire and enable individuals toward violence a "lingering phenomenon."

Comey said that the FBI currently has in the area of 1,000 open homegrown terrorism cases in the U.S. trying to determine where people are on the spectrum of "consuming poison and acting on that poison."

Speaking to the difficult nature of the current threat environment, Comey said these consumers of ISIS propaganda are people "of all backgrounds." The director said that FBI's terrorism-related cases have spanned the age range of roughly 15-60 years old, adding that there is no one particular "hot spot" in the U.S. for extremist activity because a lot of the recruitment and inspiration continues to happen online.

Comey also acknowledged instances where individuals who had prior contact with the FBI went on to carry out attacks in the U.S. Specifically, he mentioned Orlando Pulse Nightclub attacker Omar Mateen and the fact that the Bureau had already done a months-long investigation on him that "produced nothing to incapacitate him on."

Comey said that he personally reviewed the case file and called the work a "quality investigation," adding that he believes Mateen radicalized closer to the actual attack.

When asked during the Q&A portion of the event whether his public statements on the findings of the Clinton email investigation had any bearing on his decision Monday to publicly acknowledge the existence of an FBI counterintelligence investigation into Trump campaign ties to Russian officials, Comey playfully said "I'm not gonna talk about it."