NEW YORK -- CBS News has learned about a potential terror threat for the day before the election.

Sources told CBS News senior investigative producer Pat Milton that U.S. intelligence has alerted joint terrorism task forces that al Qaeda could be planning attacks in three states for Monday.

It is believed New York, Texas and Virginia are all possible targets, though no specific locations are mentioned. A U.S. law enforcement source briefed on the threat information told CBS News’ Milton that the threat is possibly legitimate and concerning. The source said the threat may be aspirational and hence the lack of specificity. The source said there has been pressure on al Qaeda and its affiliates AQAP and AQIS (al Qaeda in the Indian Subcontinent) to regain relevance with its mission.

U.S. authorities are taking the threat seriously, though the sources stress the intelligence is still being assessed and its credibility hasn’t been confirmed. Counterterrorism officials were alerted to the threat out of abundance of caution.

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“While we do not comment on intelligence matters, we will say the counterterrorism and homeland security communities remain vigilant and well-postured to defend against attacks here in the United States,” a U.S. intelligence official told CBS News. “The FBI and DHS, working with our federal, state and local counterparts, share and assess 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.

“As we have long said, in this environment, homegrown violent extremists could strike with little or no notice. Our concern that violent extremists could be inspired to conduct attacks inside the U.S. have not diminished.

“The public should expect to continue to observe an increased law enforcement and security presence across communities in public places. Our law enforcement community also continues to take action against those who attempt to engage in activities that could put Americans at risk. There are more than 100 Joint Terrorism Task Forces at work across the country in partnership with state and local law enforcement to prevent attacks in the homeland.”

The New York Police Department said it was working with intelligence agencies and the Joint Terrorism Task Force, according to the Reuters news agency.

Intelligence about potential threats always increases during holiday seasons and when big events are approaching.

As Election Day nears, federal law enforcement is planning for several worst-case scenarios.

Earlier this week, an alert warned local police of “polling places” being seen as “attractive targets” for “lone wolf”-type attacks by individuals motivated by violent extremist ideologies, sovereign citizen or other extremist activity.