Federal law enforcement officials tell ABC News a plot designed to use 15 to 20 suicide bombers on one commuter train as close to Sept. 11 as possible was well under way.
The specific target was the PATH commuter trains that run in a tunnel under the Hudson River into New York City.
"This is a plot that would have involved martyrdom, explosives and certain of the tubes that connect New Jersey with lower Manhattan," said Mark Mershon, Assistant Director-in-Charge of the FBI New York Field Office. "We’re not discussing the modality behind, beyond that."
But law enforcement officials say the plotters had already accessed detailed blueprints and drawings of the PATH tunnels, available on the internet.
And like the London bombers, the plan was to load backpacks with explosives.
All 15 to 20 bombers were to board one car and detonate when the train was under the river, according to officials.
"There’s no question that they are vulnerable. With the right amount of explosives, the tunnel could be compromised," said Jerry Hauer, former Director of New York City’s Office of Emergency Management and now an ABC News consultant.
The FBI identified the ringleader as 32-year-old Assem Hammoud of Lebanon.
Lebanese officials arrested him in April at the request of the FBI, and he reportedly has now admitted he was about to go to Pakistan for training at an al Qaeda camp. "We know that he has acknowledged pledging a bayat or allegiance to Osama bin Laden, and he proclaims himself to be a member of al Qaeda," said Mershon.
Security was stepped up today at the PATH tunnels.
Officials said today two other alleged plotters had also been arrested, but at least five of them remain at large.
"This shows we are able to disrupt terror plots such as this," said New York City Police Commissioner Ray Kelly. "Secondly, it shows that New York remains in the terrorists’ cross hairs."
Officials say the plot was uncovered more than a year ago by U.S. and Canadian intelligence agents watching a jihadist internet chat room.
Officials say the suspects communicated freely, thinking that no one could track them.
Similar chat rooms were used by the alleged terrorists arrested recently in Toronto and Miami.
"The chat rooms have literally exploded since 9/ll because we are now right in the midst of electronic jihad," said Jack Cloonan, former senior agent on the FBI’s bin Laden squad in New York and now an ABC News consultant.
Officials say none of the plotters was in the United States but that several of them were nearby in Canada. Others had planned to travel to New York from Saudi Arabia.
Officials say even after their leader was arrested in April, the plotters continued to make plans, and officials say they can’t be sure the plan is fully stopped, even now.