The US Attorney-General, Alberto Gonzales has warned that home-grown terrorists could pose as much danger to the US as foreign al-Qaeda operatives.
US officials were quick to stress the alleged plot was foiled early
Seven men have been charged with plotting to blow up the Sears Tower in Chicago, and attack FBI offices.
The men, five from the US and two from Haiti, hoped to wage a "full ground war" against the US, according to the charges brought against them.
Officials said the men were foiled at an early stage and posed no danger.
Mr Gonzales said the group of "home-grown terrorists" were inspired by "a violent jihadist message".
"They were persons who for whatever reason came to view their home country as the enemy," he told reporters.
According to charges brought against the men, the group of men aged 22 to 32 had sworn allegiance to al-Qaeda, but had no contacts with it.
They have been charged with conspiring to blow up both the Sears Tower and the FBI building in North Miami Beach.
A federal indictment says they were conspiring to "levy war against the United States".
They were arrested at a warehouse in Miami, during an undercover operation after their group was infiltrated by an agent posing as an al-Qaeda member
Mr Gonzales said the lack of direct link to al-Qaeda did not make the group any less dangerous.
"Today terrorist threats come from a smaller, more loosely defined cells not affiliated to al-Qaeda," he said.
"Left unchecked these home-grown terrorists may prove as dangerous as groups like al-Qaeda."
Five of those charged appeared at a Miami federal court on Friday.
They wore ankle chains and were chained together at the wrists, the Associated Press reported.
Alleged ringleader Narseal Batiste apparently asked an undercover agent he thought was from al-Qaeda for help to build an "army to wage jihad", the indictment said.
He is said to have told the agent he and his "soldiers" wanted al-Qaeda training and planning for a "full ground war" against the US in order to "kill all the devils we can".
Photos of the accused men were released on Friday
His mission would "be just as good or greater than 9/11", Mr Batiste said, according to the indictment.
No weapons were found in the Miami warehouse, and the seven had not posed any immediate danger, the FBI said.
Deputy FBI leader John Pistole said the plot had been "aspirational" rather than "operational".
Neighbours in Miami's poor Liberty City area said the men apparently slept in the warehouse where they were arrested.
"They would come out late at night and exercise. It seemed like a military boot camp they were working on there. They would come out and stand guard," said Tashawn Rose.
However a man claiming links to the arrested men told the news channel CNN that they were a peaceful religious group, who studied Allah.