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The FBI issued an alert to police departments nationwide warning about a potential anarchist "Halloween revolt" plot to attack cops, according to two law enforcement officials.

The officials told NBC News that police forces have been warned that members of an anarchist group called the "National Liberation Militia" might be planning to dress up in costumes, cause a disturbance then ambush responding officers.

There is no specific or credible information about when or where the so-called "Halloween revolt" plot will play out, the officials cautioned.

They told NBC News that the National Liberation Militia was a known group — though offered no other details on the group's makeup. Little record for such a group could be found online.

The New York Post was first to report news of a potential plot, saying that militia members were encouraged to wear typical Halloween masks and use bricks, bottles and firearms.

The FBI declined to comment on the contents of the bulletin, saying in a statement that it "routinely shares information about potential threats" as part of a "continuous dialogue" with law-enforcement partners.

The Los Angeles Police Department confirmed it had received the information and shared it with officers. Commander Andy Smith told NBC Los Angeles that there was not a credible threat against the city.