Story highlights There are no known specific, credible threats

The bulletin was issued out of an abundance of caution

(CNN) Federal authorities warned Friday that ISIS sympathizers "continue aspirational calls for attacks on holiday gatherings, including targeting churches."

The bulletin was issued by the FBI and Department of Homeland Security and issued to law enforcement agencies and private security companies around the US.

There are no known specific, credible threats, US law enforcement officials say. The bulletin was issued out of an abundance of caution given the public nature of the posted threats and the holiday season.

The bulletin was sent Friday to law enforcement after pro-ISIS websites had published a publicly-available list of churches in the United States.

The bulletin also describes the different signs of suspicious activity law enforcement should be aware of.

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