(CNN) -- FBI agents were raiding sites in Miami, Florida, on Thursday in connection with a domestic terrorism investigation, law enforcement sources said. Officials said no weapons or bomb-making materials had been found in the searches so far. The FBI told CNN that seven arrests were made in connection with "suspected domestic terrorist activity," and that documents related to the investigation have been sealed. The FBI said one search warrant was being executed in a warehouse near a housing project in Liberty City, a predominantly black and low-income area of Miami. "We are conducting a number of arrests and searches, and we'll have more about that when the operation is completed, probably tomorrow morning," FBI Director Robert Mueller told CNN's Larry King in an interview to be broadcast Thursday night. "Because it's an ongoing operation, we really can't get into details," Mueller said. "But whenever we undertake an operation like this, we would not do it without the approval of a judge. We've got search warrants and arrest warrants and the like. ...."
In a statement, the U.S. attorney's office in Miami said federal, state and local agencies had made several arrests Thursday in connection with a domestic "terrorist-related matter." Attorney General Alberto Gonzales will hold a news conference Friday regarding the raids.