Seven people were arrested in connection with the early stages of a plot to attack Chicago's Sears Tower and other buildings in the US, including the FBI office here, a federal law enforcement official said. As part of the raids related to the arrests Thursday, FBI agents swarmed a warehouse in Miami's Liberty City area, using a blowtorch to take off a metal door. A neighbor said the suspects had been sleeping in the warehouse while running what seemed to be a "military boot camp." The official told The Associated Press the alleged plotters were mainly Americans with no apparent ties to al-Qaida or other foreign terrorist organizations. He spoke on condition of anonymity so as not to pre-empt news conferences planned for Friday in Washington and Miami. Miami US Attorney R. Alexander Acosta said in a statement that the investigation was an ongoing operation and that more details would be released Friday.