CIA Director: ISIS Terror Attack in the US Only a Matter of Time

More details are emerging Thursday about the terror attack in Istanbul that left at least 42 dead and nearly 150 injured.

Airports around the world are increasing security and a top U.S. security official warned it's only a matter of time until terrorists attempt a similar attack here at home.

Turkish police forces are targeting Islamic State suspects in raids as investigators learn more about the coordinated attack at Istanbul's airport.

Police have learned there were three attackers, all with specific assignments. One went to the terminal, another to arrivals and a third waited outside.

The horrific terror attack in Turkey has prompted increased security at U.S. airports and is also raising familiar questions about airport security generally.

"If anybody here believes the U.S. homeland is hermetically sealed and that ISIL would not consider that, I would guard against that," CIA Director John Brennan said.

Brennan said ISIS is determined to kill as many people as possible and to carry out attacks abroad. He believes they will continue trying to penetrate American defenses.

In an interview with Yahoo News, Brennan credited effective homeland security measures and intelligence for the fact that so far the terror group has been unable to attack America directly.

The Orlando and San Bernardino shootings were carried out by radicals inspired by ISIS, but not under its direct control.

One major vulnerability terrorists took advantage of not only in Turkey but also in Belgium is the fact that most airports don't have security screening before people enter the terminals.

Former TSA official John Halinsky asked, "What's on the outside of an airport? Glass, and glass with an explosive like that is going to cause a lot more damage from a fragment standpoint. That's gonna inflict mass casualties."

Aviation security experts say one of the main lessons for other airports is to have enough armed police to regularly patrol public spaces and to keep checkpoint lines moving so crowds don't get big in vulnerable areas outside of the security perimeter – something major U.S. airports are now pledging to do.