The jihadists struck at the heart of Europe on Tuesday, hitting the Belgian capital's airport and metro system and leaving 340 people wounded, four months after the IS group claimed responsibility for coordinated deadly attacks on Paris.
Washington is leading coalition air strikes on the IS group in Syria and Iraq, but the latest attacks are another painful reminder that the jihadists remain a grave threat far beyond those war-torn countries, said Kerry.
"We've been looking for additional screening. We've been engaged actually with the Belgium authorities for some period of time now trying to fill gaps that they're aware exist."
Asked if there was a sense of urgency in Europe to plug those holes and prevent a repeat of Brussels or Paris, Kerry replied: "There's great urgency. There's a sense of urgency, clearly."
Kerry, who was in Brussels in the aftermath of the attacks, added: "The prime minister of Belgium (Charles Michel) made it very clear: they know they need to move on these things and hopefully that will happen.