NEW YORK, Aug 11: The New York city police on Friday responded to uncorroborated radiological threats reported on an Israeli website by taking extra counterterrorism precautions.

Police officials said they had not changed the city’s terror alert status in response to online chatter mentioning a truck packed with radioactive material. But police deployed extra radiological sensors on street, water and air patrols, and were stopping vehicles at checkpoints in lower Manhattan and around the city.

An official called the measures ‘strictly precautionary’.

Reuters adds: The authorities said the security had been stepped up throughout Manhattan and at bridges and tunnels in response to an internet report, which they could not verify, that Al Qaeda might be plotting to detonate a dirty bomb in the city.

Police said in a statement that the threat against the city was an ‘unverified radiological threat’ and the alert status for an attack was unchanged at ‘orange’.

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

One law enforcement source told Reuters that authorities were responding to internet chatter reported on www.debka.com.

That site reported that there had been a rush of electronic chatter on Al Qaeda sites, one saying there would be an attack “by means of trucks loaded with radioactive material against America’s biggest city and financial nerve centre”.

Another Al Qaeda message mentioned New York, Los Angeles and Miami as targets, the Jerusalem-based internet news site reported.

Police confirmed that the increased security was in response to receiving information that a dirty bomb might go off on Friday evening around 34th street in Manhattan -- a neighbourhood with the Empire State Building, Madison Square Garden and Macy’s department store.