The killing of al Qaeda leader Osama bin Laden five years ago was regarded by many as as a major turning point in the fight against terror. But over the last few years, the world has witnessed new threats, especially the rise of the Islamic State group, also known as ISIS, which, according to CIA chief John Brennan, will be a huge challenge for the counterterrorism community.

Ahead of the fifth anniversary of the killing of bin Laden, who had been eliminated in a U.S. special forces raid in Pakistan on May 2, 2011, Brennan warned that ISIS has become a “phenomenon” and taking out Abu Bakr al-Baghdadi, the head of the extremist group, would have a “great impact” on the organization. Talking on NBC’s “Meet the Press” on Sunday, Brennan said authorities needed to remain focused on destroying all the elements of ISIS, which has significant territorial advantage in Syria and Iraq.

“We have destroyed a large part of Al Qaeda. It is not completely eliminated, so we have to stay focused on what it can do. But now, with this new phenomenon of ISIL, this is going to continue to challenge us in the counterterrorism community for years to come,” Brennan said.

When asked if killing al-Baghdadi was as important as removing bin Laden from action, Brennan was affirmative.

“He's important, and we will destroy ISIL, I have no doubt in my mind. And we have to remove the leadership that directs that organization to carry out these horrific attacks,” Brennan said. “If we got Baghdadi, I think it would have great impact on the organization and it will be felt by them.”

According to Brennan, a number of individuals from outside of Syria and Iraq have travelled to join the so-called caliphate set up by ISIS, which has been successful in misleading “the hearts and minds and souls” of people who are blinded by religion. Brennan also criticized Syrian President Bashar Assad for carrying out attacks against his citizens and using chemical weapons, allowing extremists and terrorists to seize them.

“So I think ISIS was able to use those instances, whether it be in Syria, or Iraq, and abuses and corruption on the part of these governments to appeal to a broad swath of people. And so it gained strength very quickly, quicker than we thought,” Brennan said.

The CIA director’s comments came as his agency marked the five-year anniversary of the finding and killing of bin Laden Sunday by tweeting the events of the raid as it had happened. Using the hashtag #UBLRaid, the federal agency tweeted updates, including the famous photo of the Situation Room in the White House.