Officials are investigating whether a Canadian is connected to an alleged terrorist plot to bomb the train tunnels beneath the Hudson River, which is used by thousands of New York City commuters every day.

Sources confirmed to CTV that a Montreal man, who police suspected of being involved in the plan, was questioned by the RCMP but later released.

Another suspect, alleged ringleader Assem Hammoud, was held by police in Lebanon on April 6 and interrogated by the FBI. Officials said Hammoud may have spent time in Canada.

Public Safety Minister Stockwell Day refused to comment on the possible Canadian connection.

"One thing that we know is that people who plan these despicable deeds, they know no boundaries," Day said Friday at a Toronto news conference.

U.S. authorities worked with intelligence agencies in six foreign countries to crack the planned attack on the PATH rail system that links 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.

Chat rooms

FBI agents monitoring Internet chat rooms routinely used by extremist groups discovered the plot aimed at striking a blow to the city's economy by destroying its transportation network, officials said.

Three suspects are in custody abroad, one of them in Lebanon, he said.

"We believe we have what I'll call eight principal players. And that we have them largely identified." He added: "Some are in custody, one of those has been charged formally in Lebanon."

"It's our understanding at this point that none of the individuals who are, as we say, principal players in this plot have been in the United States, and they are certainly not here now," he said.

Lebanese authorities, working with U.S. law enforcement agencies, arrested an al Qaeda operative who admitted to plotting a terror attack in New York City, a senior Lebanese security official said Friday.

The arrest was reportedly made a month ago.

The suspect was at first identified as Amir Andalousli, but officials said the man was actually Hammoud, a 31-year-old Beirut native.

"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.

Hammoud told investigators he was acting "on a religious order from bin Laden and said 'I am proud to carry out his orders'," a Lebanese security official told The Associated Press.

The plot was first reported by the New York Daily News in its Friday editions, the first anniversary of the attacks on the London transportation system that killed 52 people.

The newspaper quoted unidentified counterterrorism sources as saying authorities had unearthed a plot to detonate enough explosives inside the 79-year-old Holland Tunnel to destroy it and send devastating floodwaters through lower Manhattan.

The tunnel runs under the Hudson River between New Jersey and Manhattan and carried almost 34 million vehicles in 2005.

The idea was reportedly inspired by the flooding in New Orleans from Hurricane Katrina.

The newspaper quoted experts as saying the plan to flood the financial district was badly flawed because the tunnel was protected by concrete and cast-iron steel.

The experts also said the plan was unfeasible that even if the tunnel were to crack, the financial district was above the level of the Hudson River.

A government counterterrorism official with knowledge of the probe told AP on condition of anonymity that while the alleged plot was targeting New York's transportation system, there was no evidence that the Holland Tunnel was part of the plot.

It's unclear how far along the planning for the alleged scheme was.

"At this time we have no indication of any imminent threat to the New York transportation system, or anywhere else in the U.S.," Richard Kolko, Washington-based FBI special agent, said in a statement to Associated Press Radio.

Rep. Peter King said that federal law enforcement and New York police have been monitoring a plot to attack New York's mass transit system for at least eight months.

King said he has received regular intelligence briefings as chairman of the House Homeland Security Committee.

But he did not publicly disclose what he learned to protect the integrity of the investigation, he said.

"This is ongoing, that's why I've said nothing about it until now," King said. "It would have been better if this had not been disclosed."

In its statement, the FBI and Department of Homeland Security indicated that the investigation was ongoing.

"We know al Qaeda continues to have an interest in attacking the United States,'' it added." At this point in time, there is no specific or credible information that al Qaeda is planning an attack on U.S. soil."

With files from The Associated Press