Homeland Security Secretary John Kelly said the recent attacks in Manchester, England represent a "generational struggle."

"This is just the way terrorism is today and I think it will be around for many, many years to come," Kelly said.

Speaking on Fox News Sunday, Kelly said he had now called the U.K. three times in his time in office to offer his condolences because of a terror attack.

The new tactics of terrorists mean they are now shunning massive plots like the one seen on Sept. 11, 2001, and instead terrorists are trying to pull off to smaller plots similar to Manchester.

Earlier in the week, Kelly said in congressional testimony, "As horrible as Manchester was, my expectation is we're going to see a lot more of that kind of attack."

Fox News Sunday host Chris Wallace followed up, asking, "Here in the U.S.?"

"We have no specific — we have threats all the time, but no, no right now, specific threat. But that goes to the fact that we are over here and not over there."

Kelly said that as the Islamic State was being destroyed, many former fighters are returning to places in Western Europe, which means the risk is increasing there at the moment.