Six men have been arrested on charges of plotting to attack Fort Dix army base in the US state of New Jersey.
The army base at Fort Dix is mainly used for training reservists
The men, all foreign-born and described as "Islamic militants", planned to use automatic weapons to kill as many US soldiers as possible, prosecutors say.
The FBI says it infiltrated the group after a video shop alerted the police to being asked to copy onto DVD footage of the men firing guns and chanting.
Officials say there is no evidence of links to international terror networks.
Four of the suspects were born in the former Yugoslavia, one in Turkey and one in Jordan.
The six, some of whom were in the US illegally, appeared in court in Camden, New Jersey, on Tuesday.
A spokesman for the US Attorney's Office in New Jersey, Michael Drewniak, said they faced charges of conspiracy to kill US servicemen.
'Dodged the bullet'
Speaking at a press conference in Camden, US attorney Christopher J Christie thanked the video store clerk who had alerted police after seeing the suspicious footage in late 2005.
It apparently showed 10 young men, including the six suspects arrested, firing guns as they shouted "Allah Akbar" (God is great).
He also praised law enforcement officers for working together to monitor the group for the next 16 months, before making arrests on Monday evening in Cherry Hill, New Jersey, where five of the men lived.
"We were able to do what law enforcement is supposed to do in the post-9/11 era - stay one step ahead of those who are attempting to cause harm to innocent US citizens," he said.
He said the alleged plotters had looked at other military bases in Philadelphia and Delaware before deciding on Fort Dix as a target.
They chose the New Jersey base because one of the men knew it well through delivering pizzas there, he said.
The FBI informant who infiltrated the group had recorded the suspects watching footage of other attacks against US soldiers and videos of al-Qaeda leader Osama Bin Laden, Mr Christie said.
FBI agent JP Weiss said the discovery of the alleged plot had allowed US authorities to step in during the planning stage and avoid a potentially serious attack.
"Looking at the weapons they were trying to obtain, we dodged a lot of bullets," he said.
He said the alleged plot was a reminder that the US faced the threat of "a brand new form of terrorism", where isolated groups, rather than big networks like al-Qaeda, might plan attacks.
White House spokesman Tony Snow earlier told reporters there was "no direct evidence" that the men allegedly involved in the plot had links to international terror networks.
"They are not being charged with being members of an international terror organisation," he said.
"However, their involvement in weapons training, operational surveillance and discussions about killing American military personnel warranted a strong law enforcement response."
The men allegedly trained in weapons use over recent months in the Pocono Mountains area of north-eastern Pennsylvania.
Fort Dix is used for military training, particularly for reservists.