Internet chatter about a dirty bomb threat from Al Qaeda resulted in police setting up checkpoints with radiological monitoring equipment in New York City over the weekend.

The action was taken after the Israeli website debka.com reported a spike in chatter on Al Qaeda websites referring to trucks loaded with radioactive material striking "America's biggest city and financial nerve center".

Police manned checkpoints on Friday and Saturday at roads into and out of the city, including the busy Holland Tunnel.

Of the police presence one commuter told Reuters: "I'm glad to see them here. It means they're aware of any dangers and are doing something about it."

Mayor Michael Bloomberg said that the NYPD takes such precautions "every day" against unconfirmed threats.

New York City's alert level was not raised above orange.

The term dirty bomb is used in reference to an explosive device which uses conventional explosives in tandem with radiological material.