Uniformed police officers have flooded New York City's Penn Station, home to the Long Island Rail Road, following a warning from the FBI of a "plausible but unsubstantiated" threat of a terrorist bomb attack against the system during the holidays.
Law enforcement officials tell ABCNews.com, the plot involved a "Madrid-like attack," a reference to the synchronized bombing of the commuter rail system in Spain in March 2004 that killed 191 people.
A terror suspect arrested in Pakistan by the FBI in recent days provided authorities with details of a bomb plot against the Long Island Rail Road and other information that led to series of high level intelligence and law enforcement conference calls over the past 24 hour and the issuing of a bulletin warning of an unspecified holiday attack on the New York City region's commuter rail system, ABC News has learned.
The suspect - according to some reports the arrest took place in Pakistan - recently met with Al Qaeda leaders and was able to provide authorities with significant detail as to how the plotters would have carried out an attack if their plans had gotten beyond the so-called "aspirational" stage.
Authorities had no evidence to substantiate the suspect's charges and there is no evidence of any active plot, multiple officials said.
The suspect is believed to have in the past resided in Suffolk County, Long Island. The island is a 7.5 million population peninsula that contains two boroughs of New York City - Brooklyn and Queens - as well as two suburban counties - Nassau and Suffolk, which have more than 1.4 million residents.
Federal and regional authorities are deploying additional assets throughout the North East transportation corridor today, officials said, following a 1 p.m. conference call.
Assets under consideration for including in the beefed up law enforcement presence included a new cadre of federal air marshals that will be deployed alongside Metropolitan Transportation Authority (MTA) officers in Penn Station, Grand Central Station and other locations throughout the rail corridor.
Regional and federal authorities held the first in their series of conference calls on the threat yesterday evening. Today's call members included Kip Hawley, the head of TSA, Deputy Chief Jim Waters, the New York City Police Dept. Chief in charge of the Joint NYPD-FBI Counter Terror Task force, and high level officials from the federal government.
Dept. of Homeland Security, the states of Connecticut, New Jersey, and New York, as well as representatives of New York's suburban Westchester, Suffolk and Nassau Counties, and members of various railroad police agencies.
Authorities including the New York City Police, MTA, and New York State Dept of Homeland Security said that because traditionally heavy holiday police deployments had already been anticipated, they were able to quickly move to shift deployments, increase them in some areas, and adjust their response to the preceived threat.
Following the public release of the warning by the FBI and the Department of Homeland Security, officials in Washington made efforts to dampen public concern.
"There is nothing concrete to suggest this plot ever went beyond the aspirational or talking stage," said a U.S. official familiar with the intelligence that led to the warning.
Law enforcement officials told ABCNews.com the information was based on an FBI source who has proved "reliable and knowledgeable in the past."
Officials told ABCNews.com unspecified new information in the last 48 hours led to the public warning "out of an abundance of caution."
Congressman Peter King (R-NY), the top Republican on the House Homeland Security Committee, told the Associated Press "authorities have very real specifics as to who it is and where the conversation took place and who conducted it."
The FBI's source reportedly told agents of an al Qaeda-connected group's desire to place bombs or suicide bombers inside the first and last Long Island Rail Road commuter cars and detonate them as the train entered Pennsylvania Station in Manhattan, also used by the Washington-New York-Boston Amtrak system and the New York City subway.
Senior FBI officials said their source said the group began its discussions "in late September."
The officials confirmed the nature of the plot and said that FBI agents worked through the night Monday to shape the language of a memo sent to local law enforcement.
"Transit passengers in larger metropolitan areas like New York may see an increased security presence in the coming days. This includes uniformed and plain clothed behavior detection officers, federal air marshals, canine teams, and security inspectors," said Russ Knocke, a Department of Homeland Security Spokesman. He said there were no plans to raise the current threat level.
New York City Deputy Police Commissioner for Public Information Paul Browne said in a statement: "The New York City Police Department is aware of an unsubstantiated report indicating that Al Qaeda terrorists discussed targeting mass transit in New York City and vicinity. We have no information indicating that these discussions advanced beyond the aspirational stage, but in an abundance of caution, the NYPD has deployed additional resources in the mass transit system. It is not uncommon for the department to receive threat information and to adjust our resources accordingly."
FBI and New York counter-terrorism officials involved in assessing the threat said they hardly viewed the warning as a "routine matter."
"We are coordinating and communicating with the region's transit and security agencies to provide seamless operations during this exceptionally busy time," said Michael Balboni, the NY State Deputy Secretary for Public Safety. "This is a continuation of ongoing operations that have been in place for some time, with different patrolling mechanisms to ensure the safety of mass transit."
The FBI warning was made public on the morning of the busiest travel day in the country. Many New York commuters leave their city jobs early on Thanksgiving eve.