CNN reports:

New intelligence indicates al Qaeda is threatening to attack corporate and financial institutions in New York City, a federal law enforcement official told CNN on Saturday.

The official said the information suggests “there is a new plan in the works.”

On TV, the CNN reporter specified that this threat is seemingly being taken more seriously than some of the vague and/or uncorroborated threats we’ve heard about before. The New York Times confirms this:

“The information is considered credible,” said another law enforcement official, who insisted on anonymity. The official said the police and federal terrorism authorities, who have received similar threats before, were unusually concerned about the new information.

ABC News, which apparently broke this story, states that “Wall Street firms may be among the targeted U.S. corporations based in New York City. Which corporations or how many may be targeted has not been revealed.”

“It would be right to assume that there is particular concern” about large Manhattan buildings and institutions, according to the a law enforcement source who spoke with the Times. He said the United Nations was considered a potential target, as were large banks, financial institutions and company headquarters.”

Officials suspect a Mexican connection, which is especially intriguing in light of my previous post about possible illegal immigration across the Arizona border in recent weeks by groups of Arabic-speaking men. Says ABC:

Intelligence sources say al Qaeda plans to move non-Arab terrorists across the border with Mexico.

Authorities already have in custody a woman of Pakistani origin arrested after crossing into Texas. She carried a South African passport with several of the pages torn out, $7,000 in cash and an airplane ticket to New York.

The Times says the woman, Goolam Mohamed Ahmed, was arrested on July 19 after “crossing the Rio Grande and crawling through the brush.” According to one official, she is “believed to have been on a terrorist watch list”:

She might have been sent as “a courier” to pass along either a message or documentation to someone in the United States.

A law enforcement official in New York said, “the concern was that she may be part of a team” planning attacks in the city.

As for the possible method, “the attack may involve one or more suicide truck bombings, a tactic never seen in the United States, but one widely used by terrorists elsewhere,” according to ABC:

“I think they want to try and shake our psyche again,” says Jerry Hauer, an ABC News consultant and former director of New York City’s Office of Emergency Management. “And I think the easy types of attacks right now are car bombs, truck bombs.”

Law enforcement officials acknowledge such bombs are extremely difficult to prevent.

The Times’s source “said many companies and institutions had already been contacted, and that they were warned to pay particular attention to their parking garages and heating, ventilation air conditioning systems.”

CNN elaborated on those latter areas of concern, which seem to indicate a fear of possible chemical or biological attack. Companies have reportedly been advised to consider:

* Posting security at the fresh-air intake in heating, ventilation and air conditioning rooms, if they are accessible to the public, and keep the rooms locked

* Challenging maintenance workers when maintenance has not been requested, and watching for unexpected deliveries

* Testing alarm systems, including those on rooftop doors

“As to the timing of any planned attack, sources say it could take place between now and Election Day in November,” ABC reports. Of course, the Republican National Convention is in New York during the last week of August, “but it was unclear yesterday whether the new information” is tied to the RNC or any other specific timetable, according to the Times.