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.
The report triggering the security hike came from Israeli website www.Debka.com, which reported that there has been a rush of electronic chatter on al-Qaeda sites, one saying there would be an attack "by means of trucks loaded with radio-active material against America's biggest city and financial nerve center."
Another al-Qaeda message mentioned New York, Los Angeles and Miami as targets, the Jerusalem-based DEBKAfile reported.
Security guards at improvised roadbloak in NY (archive photo: AFP)
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.
The New York Police Department said in a statement it had increased the deployment of radiological sensors on vehicles, boats and helicopters, and had set up vehicle checkpoints in lower Manhattan's financial district and at bridges and tunnels.
Police confirmed the increased security was in response to receiving information that a dirty bomb may go off on Friday evening around 34th street in Manhattan - a neighborhood with the Empire State Building, New York City's tallest building, Madison Square Garden and Macy's department store.
A spokesman for the Department of Homeland Security in Washington said the threat to New York was "unsubstantiated" and there was "no credible information telling us there is an imminent threat to the homeland at this time."
New York has remained on an orange alert - the second highest such level, below red - since the September 11, 2001, attacks that destroyed the World Trade Center.