Intelligence officials have warned al Qaeda could be planning terror attacks in several states around the US presidential election.

The FBI and the New York Police Department said they are taking the threat seriously and are assessing the credibility of a possible attack on the eve of Election Day. 

Officials said counter-terrorism investigators are reviewing information that the militant group is planning to strike in New York, Texas and Virginia - although there have been no specific areas mentioned.

It is not immediately clear how the intelligence came to the attention of investigators and an NYPD spokesman has said the information "lacks specificity."

Steve Coleman, a spokesman for the Port Authority of New York and New Jersey - which operates airports, tunnels and bridges around New York City - declined to offer specifics of the warning but confirmed the authority had been alerted.

"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 said.

The threat comes just four days before polls officially open in the US.

Earlier this week, an alert warned local police that "polling places" could be seen as "attractive targets" for "lone wolf" attacks.

Officials said they regularly assess all possible security threats ahead of major events.

"The counter-terrorism and homeland security communities remain vigilant and well-postured to defend against attacks here in the United States," a senior FBI official told CBS News.

"The FBI, working with our federal, state and local counterparts, shares and assesses intelligence on a daily basis and will continue to work closely with law enforcement and intelligence community partners to identify and disrupt any potential threat to public safety."

Al Qaeda, and its now deceased leader Osama bin Laden, was behind the 11 September 2001 attacks on the US, which killed nearly 3,000 people.

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