Islamic State (ISIS) poses a direct threat to America, US Attorney General Loretta Lynch said Sunday, with the greatest danger being the possibility that the terror group develop cyber warfare capabilities.

"Concern that ISIS or any of our foreign enemies might develop that capacity...is the thing that keeps me and many of my colleagues in law enforcement up at night," Lynch told ABC's "This Week" TV show.

Lynch warned that ISIS has "a different model from other terrorist groups," making it difficult to halt its attempts to instigate terror attacks on American soil.

The key difference, she said, is that ISIS has over 20,000 English-language Twitter followers. The organization recruits people to attack on ts behalf and then takes credit, she said.

"I think that it makes it harder to predict," she said. "I think it makes it harder to determine who's going to succumb to the propaganda."

Lynch also admitted that stopping "lone wolf attacks" is very difficult for federal agents, taking as an example Muhammod Youssuf Abdulazeez's attack in Chattanooga, Tennessee on July 16, in which he murdered five marines.

"That he was not on law enforcement's radar illustrates the concern that we have of individuals who are outside the mainstream, yet tap into these strands of thought or schools of thought that lead them to violence," said Lynch.

While authorities have not publicly announced the motive of Abdulazeez's attack on army sites, his father was a Palestinian Arab who previously was on the US terrorist watch list, and the young Abdulazeez reportedly was "upset" about last summer's war in Gaza.

He also posted cryptic Islamic posts before the attack and previously spent several months in the Middle East.

Republican presidential candidate Senator Ted Cruz (R-TX) condemned the American response to the attack, declaring it a radical Islamic "act of war."