By David Ingram

NEW YORK (Reuters) - Federal officials have warned authorities in New York, 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 U.S. 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.

The New York 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 specifics of 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 it was working with intelligence agencies and the Joint Terrorism Task Force.

Texas Governor 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.

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 FBI 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.

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CBS News first reported the threat of attacks, which it said were possible on Monday, the day before the U.S. 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 and John Walcott in Washington, Nate Raymond in New York; Writing by Doina Chiacu; Editing by Jeffrey Benkoe and Alistair Bell)