Terror attacks are spreading in part because the enemies of the Islamic State group are playing defense rather than offense, the former director of the U.S. National Counterterrorism Center said Wednesday.
Michael Leiter, now head of integration at defense company Leidos, made the assessment one day after a terror attack at Istanbul Ataturk Airport killed 41 people. Turkish Prime Minister Binali Yildirim said the Islamic State is a prime suspect, though the Syria-based militant group has not claimed responsibility for the assault.
The strike in Turkey follows deadly ISIS-orchestrated attacks in Paris and Brussels, as well as mass shootings in San Bernardino, California, and Orlando, Florida, carried out by individuals inspired by the Islamic State.
"There is no silver bullet on this front. There are no walls to build. There is no instant change that we will do on any front. This is a multifaceted problem, and like most hard problems, it requires a lot of focused effort on a lot of different fronts," Leiter told CNBC's "Squawk Box."
He laid out four of those fronts Wednesday.
First, the United States must take a more aggressive stance in Iraq and Syria, where the Islamic State has established a self-proclaimed caliphate.
In April, President Barack Obama announced he would send more special forces troops to Syria and additional soldiers to Iraq. Still, Leiter said the U.S. has been slow in accelerating its involvement.
Second, NATO must remain "incredibly strong" in order to protect Turkey's borders and screen people effectively, even as the European Union faces challenges.
Third, the U.S. must continue to protect real targets, particularly by expanding security perimeters at airports.
Lastly, America must be deeply engaged with the Muslim world and its own Muslim population. Law enforcement should continue to form partnerships with American Muslims, as it has since the Sept. 11 attacks, Leiter said.