WASHINGTON — In the wake of the Nov. 13 terrorist attacks in Paris, the head of the Central Intelligence Agency believes there are more attacks "in the pipeline" from the Islamic State group, better known as ISIS or ISIL.

John Brennan, speaking Monday at the Center for Strategic and International Studies, also warned that the Nov. 6 terrorist attacks in Paris attacks cannot be considered "a one-off event," adding "I would anticipate this is not the only operation ISIL has in the pipeline."

"It's clear to me ISIL has an external agenda and they are determined to carry out these type of attacks," Brennan said. "It's not just Europe. I think we here in the United States also have to be, obviously, quite vigilant."

While claiming it is "inevitable ISIL and other terrorist groups will continue to try and carry out these attacks," Brennan said it was "not inevitable that they are going to succeed."

Asked how the US and global intelligence services missed the Paris attack, Brennan said, "it's not a surprise that this attack was carried out," citing some form of "strategic warning" the intelligence community had ahead of time.

However, the ability of French intel to "monitor and surveil individuals who have traveled back and forth" between France and ISIL territory in Syria and Iraq has been degraded in the last few years, something that coincides with a growing understanding of operational security among ISIL.

Since the Paris attacks, experts have pointed to the use of non-traditional communication devices, such as the Playstation network and the communications app WhatsApp, as a way for terrorist groups to communicate across distances.

Although he did not come out and specifically say it, Brennan hinted part of the blame for that growing sophistication can be laid among these groups falls at the feet of groups like WikiLeaks and Edward Snowden, whose disclosures have allowed terrorist networks to have "gone to school" on how to avoid US intelligence.

Twitter: @AaronMehta