Federal officials have warned authorities in New York City, Texas, and Virginia about an unspecific threat of attacks by the Al Qaeda militant group around Election Day, putting local law enforcement on alert the weekend before Tuesday's vote, officials said on Friday.
A US government source in Washington said some federal agencies sent bulletins to local and state officials flagging the information but that the threat was relatively low-level.
A US official familiar with the threat information said that it was "uncorroborated," but that federal agencies believed that they needed nonetheless to remain vigilant.
The New York City Police Department and the Port Authority of New York and New Jersey were alerted to the information, the local agencies said.
The Port Authority, which operates airports, tunnels and bridges around New York City, is continuing high levels of patrol it has had in place, said spokesman Steve Coleman.
He declined to offer details on the warning, but the police department said the threat report lacked specifics and was still being assessed.
"We are aware of the information," the department said in a statement, adding that it was working with intelligence agencies and the Joint Terrorism Task Force.
Although some of the attention of US authorities has shifted to Islamic State-inspired attacks, the Al Qaeda network has shown resilience more than 15 years after it was responsible for the Sept. 11 attacks on New York and the Pentagon.
Last month, the United States carried out strikes in Afghanistan targeting two of Al Qaeda's senior leaders in the country, and Al Qaeda's Yemen branch has posed a risk to merchant ships in waterways nearby.
"We still view al-Qa'ida and the various al-Qa'ida affiliates and nodes as a principal counterterrorism priority," Nicholas Rasmussen, director of the U.S. National Counterterrorism Center, told the Senate's homeland security committee in September, using an alternative spelling for the group.
Texas Gov. Greg Abbott said his office was monitoring the situation. "Texans should go about their daily lives as usual, but remain vigilant over the next several days and report any suspicious activity," Abbott, a Republican, said in a statement.
Virginia Gov. Terry McAuliffe, a Democrat, is constantly monitoring state's security, spokesman Brian Coy said. "We are doing everything we can to keep Virginians safe, and we're confident they are going to be able to vote safely on Election Day," Coy said in a phone interview.
The task force issued a notice identifying the three states as possible targets of an al Qaeda plot, a New York law enforcement official said on condition of anonymity. The official said the type of threat was common but authorities were giving it more attention because of Election Day.
Authorities were assessing whether there was a plot and whether the states named were real targets or misdirection. "Another possibility is that this is just an attempt to inspire someone here to mount an attack," the official said.
The Federal Bureau of Investigation did not confirm the reports or comment on details. Officials at the U.S. Department of Homeland Security did not respond to a request for comment.
CBS News first reported the threat of attacks, which it said were possible on Monday, the day before the US presidential election.
The potential for violence related to the election has already darkened a rancorous presidential race between Democrat Hillary Clinton and Republican Donald Trump, on top of the threat of computer hacking and fears that Russia or other state actors could spread political misinformation online or tamper with voting.
While federal and state authorities are beefing up cyber defenses against electronic threats to voting systems before Election Day, others are taking additional steps to guard against possible civil unrest or violence.
Additional reporting by Mark Hosenball, John Walcott and Ian Simpson in Washington and Nate Raymond in New York.