NEW YORK - US authorities thwarted a foreign-based plot to stage a suicide bombing of a rail tunnel in New York later this year and three suspects are being held abroad, one of them in Lebanon, US officials said today.

They said the plot was still in the planning stage and that those involved had not done any reconnaissance or obtained weapons. An FBI official said none of the suspects had ever been in the United States.

US authorities worked with intelligence agencies in six countries to crack the planned attack on the PATH rail system linking Manhattan and New Jersey under the Hudson River, said Mark Mershon, assistant director-in-charge of the FBI New York Field Office.

"This is a plot that would have involved martyrdom, explosives and certain of the tubes that connect New Jersey with Lower Manhattan. We're not discussing the modality beyond that," Mershon told a news conference.

The attack was planned for October or November, and the investigation of it began about a year ago, he said.

The FBI and Department of Homeland Security called the plotters a "terrorist network," and Lebanese officials said the suspect in custody there had confessed, calling himself the mastermind of the plot and pledging allegiance to al Qaeda and Osama bin Laden.

"We believe we have what I'll call eight principal players and that we have them largely identified," Mershon said, adding that the suspects were on three continents. He declined to disclose the nationalities of the suspects.

"We don't have charges pending in the US so there certainly will be no extradition," he said.

A Lebanese government source in Beirut told Reuters authorities there had arrested 31-year-old Assem Hammoud, also known as Amir al-Andalousi, and said he was "a suspect in a plot to bomb a tunnel in New York."

"After questioning he confessed ... that he was planning to travel to Pakistan for four months training and that the date for the attack was decided to be late in 2006," Lebanon's Interior Ministry said in a statement.

An initial report of the plot in New York's Daily News had said the target was the car-carrying Holland Tunnel.

The newspaper said the intent was to flood the Wall Street financial district, but experts said such a blast would not have flooded areas above the water level. Wall Street is some three km from the tunnel, which is dug under bedrock and reinforced with concrete and steel.

The plot was uncovered by monitoring internet chat rooms, the Daily News reported. The report was published on the first anniversary of the London suicide bombings on trains and a bus that killed 52 people.

It was the second recent domestic threat authorities have said they broke up in the early stages, following the arrest of seven people last month on suspicion of a plan to attack the Sears Tower in Chicago. One official described that plot as being "more aspirational than operational."

The PATH - Port Authority Trans-Hudson - system maintains three Hudson River tunnels, two of which connect New Jersey with Lower Manhattan through the former World Trade Centre site. A third goes to midtown Manhattan via Greenwich Village.

The tubes, which date to the early 1900s, have long been considered a soft target by security experts.

The PATH carries an estimated 215,000 passengers each weekday, according to the Port Authority.

- REUTERS