(CNN) The FBI and Department of Homeland Security are warning law enforcement ahead of the opening weekend of the movie "Joker" after a number of threats were posted online calling for mass shootings at showings of the movie.

In a Joint Intelligence Bulletin shared with police this week and obtained by CNN, federal authorities write that the FBI has no information leading to "specific or credible threats to particular locations or venues," but note that the FBI has received tips of threats posted on social media since at least May.

There has been a heightened level of concern about the movie's premiere because of the 2012 mass shooting at an Aurora, Colorado, movie theater on the opening night of another Batman movie.

Twelve people were killed and 70 wounded in that attack, at a midnight showing of "The Dark Knight Rises."

Concern from law enforcement has been growing in recent weeks ahead of the movie's premiere. The Army said over the weekend it had warned soldiers at at least one base, in Fort Sill, Oklahoma, about the threats, and the Los Angeles Police Department has said it will have "high visibility" at theaters showing the movie.

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