Seven members of the radical Black Muslim group were arrested in Miami for allegedly plotting terrorist strikes at various targets including Chicago's Sears Tower and FBI building in Miami.
Law enforcement officials said the plot was still in early stages and during searches no bombs, weapons or bomb making materials were found.
The men were Americans and had no direct links with Al-Qaeda but one of them was said to have taken Al-Qaeda oath, officials said.
The group had carried out surveillance of at 110-floor Sears Towers, the tallest skyscraper in the US, at 435 meters.
The arrests came after a month-long undercover operation when the FBI infiltrated into the group.
The threat level to the Miami and Chicago was not raised as the officials said they were not in immediate danger and the plot had been disrupted in the early stages.
FBI agents used a blowtorch to take off the metal door of a warehouse in a poor back neighbourhood in Miami, which they searched.
The arrested are expected to be indicted on the charges of attempting to "maliciously damage or destroy" property by an explosive device.
"There is no imminent threat to Miami or any other area because of these operations," Richard Kolko, spokesman for FBI headquarters in Washington, told media.
"It would be inappropriate for us to confirm or deny the details of the news reports about federal law enforcement action before an official statement from Justice Department," CNN quoted managing director of the Sears Tower Barbara Carley as saying.