Via FOX News:
With as many as 1,000 active cases, Fox News has learned at least 48 ISIS suspects are considered so high risk that the FBI is using its elite tracking squads known as the mobile surveillance teams or MST to track them domestically.
“There is a very significant number of people that are on suspicious watch lists, under surveillance," Republican Sen. Dan Coats said.
Coats, who sits on the Select Committee on Intelligence, would not comment on specifics, but said the around-the-clock surveillance is a major commitment for the bureau. "The FBI together with law enforcement agencies across the country are engaged in this. It takes enormous amount of manpower to do this on a 24-7 basis. It takes enormous amount of money to do this," Coats explained.