The 90-page "Radicalization in the West and the Homegrown Threat" study said the clusters are formed in such places as mosques, bookstores, cafes and prisons, calling them "radicalization incubators" that provide "extremist fodder or fuel for radicalization," ABC News reported.

The report said various law enforcement agencies have identified the groups, which it said are on a path to spawning homegrown terror activities.

"Any one of those clusters may be capable of carrying out a terrorist action that will result in fatalities," Rand Corporation terrorism expert Brian Jenkins told the network. "The threat is real; this is not some bogey man we are creating here. There are individuals who are proselytizing, inciting angry young men to go down this path."

Kareem Shora, executive director of the American Arab Anti-Discrimination Committee, called the report "un-American" and said it would make things worse.

"We do not want to alienate any segment of any community and by using that language you are actually aiding the extremists in their recruiting efforts," Shoraa told ABC News.