Seven men were charged last night with conspiring to blow up the landmark Sears Tower in Chicago and the FBI building in Miami in a mission they hoped would be "just as good or greater" than September 11th, US officials said.
But Attorney General Alberto Gonzales told a news conference in Washington that the plotting by the "home-grown terrorism cell" never went beyond the earliest stages.
"There was no immediate threat,"Mr Gonzales said, acknowledging the defendants never had contact with al Qaeda and did not have weapons or explosives.
Deputy FBI Director John Pistole said at the Justice Department news conference that the discussions to attack the 110-story Sears Tower - the tallest building in the United States - were "aspirational rather than operational."
In a Florida grand jury indictment issued on Thursday, the men are accused of pledging loyalty to Osama bin Laden's al Qaeda to seek support from it for their desire to "wage war" against the US government and build an Islamic army.
They wanted to "kill all the devils we can," it said. But a person they thought was an al Qaeda representative was actually an FBI informant, justice officials said.
The raid on the Miami-based group grabbed the national media spotlight but officials denied there was any political motivation before midterm congressional elections in November, amid a deep slump in President George W. Bush's popularity and in public support for the Iraq war.
Critics of the administration frequently accuse it of exploiting fear of a repeat of the September 11th attack.
"These are precisely the types of groups that we should be dismantling and disrupting and we are going to continue to aggressively pursue any cell that expresses an intent to commit terrorist acts against the US," said R. Alexander Acosta, US Attorney for the Southern District of Florida.
The markets shrugged off news of the arrests.
Five of the men - suspected ringleader Narseal Batiste, along with Patrick Abraham, Rotschild Augustine, Burson Augustin and Naudimar Herrera - appeared briefly in a Miami magistrate's court on Friday. Shackled and dressed in khaki prison garb with plastic sandals, they were granted court-appointed attorneys.