US intelligence officials have warned officials in New York, Texas and Virginia about possible attacks by al Qaeda in the run up to Election Day.

No specific locations were mentioned, but intelligence officials alerted joint terrorism task forces about the threat.

The Port Authority of New York and New Jersey, which operates airports, tunnels and bridges around New York city said they will continue with "high level of patrols".

Authority spokesman Steve Coleman said: "We are continuing with the high level of patrols at all of our facilities that we have had in place for some time now".

He declined to offer specifics of the warning.

In a statement, the FBI said: "The counterterrorism and homeland security communities remain vigilant and well-postured to defend against attacks here in the United States."

The bureau said they were working closely with federal, state and local law enforcement to identify and disrupt any potential threat.