CIA director John Brennan
CIA director John BrennanReuters

Iraq and Syria have been so thoroughly damaged by warfare, sectarian conflict and killing that it is unclear they "can be put back together again," CIA Director John Brennan says.

In an interview with the CTC Sentinel, a publication from the West Point military academy's Combating Terrorism Center, the head of the Central Intelligence Agency said the current system of governance in the two countries might change altogether.

"I don't know whether or not Syria and Iraq can be put back together again. There's been so much bloodletting, so much destruction, so many continued, seething tensions and sectarian divisions," Brennan said in the interview, which was quoted by AFP.

"I question whether we will see, in my lifetime, the creation of a central government in both of those countries that's going to have the ability to govern fairly," he added, noting that he could envision some type of a federal structure governing autonomous regions.

In northern Iraq and parts of Syria, for instance, Kurdish populations already have established de-facto states.

Brennan also described how the Islamic State group (ISIS) is now collaborating in Yemen with rivals Al-Qaeda to fight common enemies, such as the Houthi rebels and Arab coalition-backed government forces.

"The farther away you get from that (ISIS) heartland of Syria and Iraq, the more likely you're going to see collaboration between Al-Qaeda elements, (ISIS) elements, and others," he said.

"We see it right now in Yemen.... There are indications that, in fact, they're working together," added Brennan.

On Thursday, speaking at a conference in Washington and quoted by Reuters, Brennan predicted ISIS will remain a presence inside Syria and Iraq for "quite a while to come" despite the battlefield defeats it has suffered.

"I do think a number of them are going to remain a challenge for the United States as well for other governments for a number of years to come," he said.

Speaking at the same conference and quoted by The Associated Press, FBI Director James Comey made the same assertion.

"The threat that I think will dominate the next five years for the FBI will be the impact of the crushing of the caliphate, which will happen," he said, adding, "Through the fingers of that crush are going to come hundreds of hardened killers, who are not going to die on the battlefield. They are going to flow out."

Comey predicted that many will head into western Europe and will try to duplicate recent attacks in Paris and Brussels to maintain ISIS' credibility in the militant world. Others will try to bring the fight to the United States, making it imperative for the U.S. to help its European allies share intelligence better among themselves and with the United States, Comey predicted.