Holder: Homegrown terrorists a major concern

U.S. Attorney General Eric Holder says the growing number of American citizens joining terrorist groups including al-Qaida is "one of the things that keeps me up at night."

"You didn't worry about this even two years ago - about individuals, about Americans, to the extent that we now do," Holder said in an interview with ABC News that aired Tuesday. "And that is of great concern."

Attempted attacks in New York, Portland, Ore., and Detroit, among other cities, have put the Justice Department on alert, the attorney general said.

Holder continued: "The threat has changed from simply worrying about foreigners coming here, to worrying about people in the United States, American citizens - raised here, born here and who, for whatever reason, have decided that they are going to become radicalized and take up arms against the nation in which they were born."

Holder said one of his biggest concerns is radical cleric Anwar al-Awlaki, an American citizen believed to be in Yemen, who has played a role in coordinating efforts to recruit Americans to al-Qaida.

Holder says al-Awlaki has a familiarity with the United States that terrorists usually lack.

"He would be on the same list with bin Laden," Holder said. "He's up there. I don't know whether he's one, two, three, four - I don't know. But he's certainly on the list of the people who worry me the most."

In the interview, Holder said the terrorism threat is real and constant.

He says he's concerned that the authorities may have missed a signal that an attack is coming.

Americans have to be prepared, he said, for "potentially bad news."