Federal officials have warned New York City authorities about possible 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.

Both the New York Police Department (NYPD) and the Port Authority of New York and New Jersey were given the information, the local agencies 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,” said spokesman Steve Coleman of the Port Authority, which operates airports, tunnels and bridges around the New York City area.

He declined to offer specifics of the warning.

The NYPD said the threat report lacked specifics and was still being assessed.

"We are aware of the information. We have been working with the FBI through the Joint Terrorism Task Force and our Counterterrorism and Intelligence Bureaus," the NYPD said.

The United States has collected intelligence about a possible al Qaeda threat to attack around election time. As a consequence, some agencies sent bulletins to local and state officials flagging the information, a U.S. government source in Washington told Reuters.

The source said, however, the nonspecific threat was relatively low level.

CBS News reported earlier Friday that U.S. intelligence officials have warned local authorities in New York, Texas and Virginia about possible attacks by al Qaeda on Monday, a day before the U.S. presidential election.

CBS cited unidentified sources and no specific locations within those states.

The FBI did not comment on details of the CBS report. "The counterterrorism and homeland security communities remain vigilant and well-postured to defend against attacks here in the United States," it said in a statement on Friday.

Officials at the U.S. Department of Homeland Security did not respond to a request for comment.

The potential for clashes 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.

And 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.