(CNN)– Europe needs to work harder at defeating ISIS, Defense Secretary Ash Carter said Wednesday in the wake of the terrorist attacks in Brussels.

Carter told CNN’s Carol Costello that the suicide bombings in the Belgian capital Tuesday are a stark indicator of the necessity of defeating the terror group.

“The thing that I think the Brussels event is going to further signify to Europeans is that they — as we have been accelerating our campaign to defeat ISIL in Syria in Iraq and elsewhere — they need to accelerate their efforts and join us,” Carter said, using another acronym for the terror group.

But Carter also acknowledged that the fight goes beyond the Middle East, Iraq and Syria, which Europeans are well aware of.

“It is not enough that we defeat them in Iraq and Syria. What Brussels tell us is that they have sympathizers, people who are Belgians or French, who live there already. Therefore an important part of the fight is also going to be a homeland security, intelligence and law enforcement fight,” Carter said.

He noted that the U.S. has fewer self-radicalized individuals who travel to Syria and commit terror, but said that the law enforcement and intelligence community is on alert for such home-grown threats.

The-CNN-Wire ™ & © 2016 Cable News Network, Inc., a Time Warner Company. All rights reserved.