Federal authorities are investigating a possible threat from al-Qaeda to carry out pre-election terror attacks, leading officials in at least three states to take precautions, according to federal and state officials.

The nature of the threat, which CBS News reported first, remains vague, and local and federal authorities said they are still assessing whether or not it is credible. A federal official and state authorities said law enforcement in New York, Texas and Virginia had been notified of the possible danger and were working with their federal counterparts.

“In every case, we take any intelligence reports regarding New York City seriously,” Stephen P. Davis, the New York Police Department’s chief spokesman, said in a statement. “Our security remains a shared responsibility. We continue to encourage anyone with any information that could be relevant to the safety of our city to contact law enforcement.”

The FBI and the Department of Homeland Security each issued statements saying they were “vigilant and well-postured to defend against attacks here in the United States,” and that they “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.”

U.S. officials say the plot appeared to emanate out of a group of al-Qaeda leaders in Afghanistan.

On Oct. 23, U.S. military airstrikes killed two al-Qaeda leaders in Kunar province, Afghanistan. U.S. officials said they believed those al-Qaeda leaders may have been involved in the alleged plot.

Authorities frequently analyze nebulous threats of terror plots — and they take them especially seriously during high-profile events such as elections — but they are often unfounded. And U.S. intelligence agencies say it would be difficult for al-Qaeda’s leaders in Afghanistan and Pakistan to conduct attacks outside the region. The group has been decimated by U.S. airstrikes on both sides of the Afghanistan-Pakistan border in recent years.

There has been significant concern this year, though, about outside efforts to impact the election. U.S. officials have warned that Russia, which they say hacked the computers of the Democratic National Committee and other political organizations to interfere with the election process, may continue meddling after the election is over to sow doubts about the legitimacy of the result.

White House press secretary Josh Earnest told reporters that he did not have any intelligence assessment to give about the potential threat of an Election Day attack, but he said national security officials were mindful of the risks that come with major events.

State officials indicated they were taking the threat seriously, even though information remained scant. Texas Gov. Greg Abbott (R) issued a statement on the “Texas terror threat,” saying that his office was monitoring the situation and working with law enforcement officials, including the Texas Department of Public Safety.

“Texans should go about their daily lives as usual, but remain vigilant over the next several days and report any suspicious activity to state or local law enforcement,” Abbott said. “The state of Texas will continue to do everything it can to ensure the safety and security of its citizens.”

New York Mayor Bill de Blasio (D) said Friday that he had known about the threats “for several days” after receiving classified briefings.

“We are still very much assessing the credibility,” de Blasio said during an appearance on WNYC. “It’s not at all clear how credible this is. And it is not overly specific information so far.”

De Blasio said New Yorkers should expect an “extensive” police presence in the coming days, due to the New York City Marathon scheduled for Sunday and Election Day following on Tuesday.

He also noted that when the bitter presidential campaign ends Tuesday, both major party candidates — Hillary Clinton (D) and Donald Trump (R) — plan to hold their election night events in Manhattan at venues just two miles apart.

“We are watching carefully,” de Blasio said. “We’re certainly in a vigilant position.”

Officials responsible for key transportation infrastructure in the Northeast were also alerted. The Port Authority of New York and New Jersey, which operates the three major airports in the New York City area along with major bridges and tunnels, said it was made aware of the threats through its participation in the FBI’s Joint Terrorism Task Force.

“We are continuing to maintain a high level of security at all of our transportation facilities in the New York-New Jersey region, which has been in place for many months,” said Steve Coleman, a spokesman for the Port Authority.

In Virginia, the office of Gov. Terry McAuliffe (D) referred a question to the state’s Department of Elections, which said in a statement that it was working “with our local, state, and federal partners to ensure the safety and security of our electoral process, as we have been for months.”

“We remain extremely vigilant for any potential threats to the upcoming election and are working with our law enforcement partners to ensure an appropriate response,” the department said in a statement. “Virginia voters should be confident that they will be able to safely cast a ballot on Tuesday and that their votes will be accurately counted.”

Adam Entous contributed to this report.

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