ISIS, as well as other terror groups, is building a network of radicalized supporters in the U.S. that is cause for growing concern, according to former U.S. Attorney General Michael Mukasey.

Mukasey, who served during the George W. Bush administration, told FoxNews.com there should be increasing emphasis on the fight against terror sympathizers and their connections stateside.

Mukasey believes, however, that this is more challenging for law enforcement to tackle and points to the First Amendment.

“So long as you can’t show that the incitement is such that it will produce an immediate result or so long there is time for reason to intervene, you really can’t stop that.”

Mukasey says U.S. officials can “monitor it and expose it and it’s ultimately up to the democratic process that will have to deal with that.”

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Critics contend that if a person is exposed continuously to hateful rhetoric it could provoke them to act violently. U.S. officials have to act cautiously when deciding whether to act.

“What you can’t criminalize is the kind of speech and hateful incitement that will percolate and that will eventually get to someone’s psyche, that you need to fight with other speech,” said Mukasey.

He believes there are a number of hotspots across the U.S. preaching an anti-American, anti-Western agenda that could be connected with associates in the Middle East.

“[They] are well-funded, if not by Saudis, by people from the Gulf that are designed to essentially teach that a lot of the concepts we have come to learn mean violent things in Islam that they are very innocuous and try to moderate that lesson and that, too, is a very dangerous phenomena.”

Mukasey added, “It used to be thought that we couldn’t have the kind of violence overseas …because you need a support mechanism around you to do that. It turns out that is probably not the case.”

Chris Snyder is a producer for FoxNews.com based in New York. Follow him on twitter: @ChrisSnyderFox