The often-unreliable unofficial Mossad outlet Depkafile has reported:

The threat was picked up by DEBKAfile’s monitors from a rush of electronic chatter on al Qaeda sites Thursday, Aug. 8.

The al Qaeda communications accuse the Americans of the grave error of failing to take seriously the videotape released by the American al Qaeda spokesman Adam Gaddahn last week. “They will soon realize their mistake when American cities are hit by quality operations,” said one message.

Another said the attacks would be carried out “by means of trucks loaded with radio-active material against America’s biggest city and financial nerve center.”

A third message mentioned New York, Los Angeles and Miami as targets. It drew the answer: “The attack, with Allah’s help, will cause an economic meltdown, many dead, and a financial crisis on a scale that compels the United States to pull its military forces out of many parts of the world, including Iraq, for lack of any other way of cutting down costs.”

There is also a message which speaks obliquely of the approaching attacks easing the heavy pressure America exerts on countries like Japan, Cuba and Venezuela.

DEBKAfile’s counter-terror sources and monitors say there is no way of gauging for sure how serious these threats are, how real, or whether they are part of a war of nerves to give the Gaddahn tape extra mileage. But it is important to note that the exchange of messages took place over al Qaeda’s internal Internet sites and that they contained the threat of radioactive terror and specific American cities for the first time after a long silence on these subjects.

In addition, a growing number of clips has been disseminated of late over al Qaeda sites instructing the faithful how to design remote-controlled gliders, pack them with explosives and launch them against predetermined targets.

Adam Gaddahn videotape summarized.

Reuters reports that New York City is responding to the Depkafile report.

New York police stepped up security throughout Manhattan and at bridges and tunnels on Friday in response to an Internet report — which authorities said they could not verify — that al Qaeda might be plotting to detonate a dirty bomb in the city.

New York City police said in a statement the threat against the city was an “unverified radiological threat,” stressed the increased security was precautionary and said the city’s alert status for an attack was unchanged at “orange.”

New York Mayor Michael Bloomberg stressed there was no reason to believe this threat was any different from countless others since the September 11 attacks.

One law enforcement source told Reuters that authorities were responding to Internet chatter reported on Israeli Web site www.debka.com, but that the information reported there could not be verified.