U.S. federal authorities cautioned local law enforcement on Friday to be aware that supporters of Islamic State have been calling for their sympathizers to attack holiday gatherings in the United States, including churches, CNN reported.

The warning, issued in a bulletin to local law enforcement, said there were no known specific, credible threats, CNN said.

The notice from the Federal Bureau of Investigation and Department of Homeland Security was issued out of an abundance of caution after a publicly available list of U.S. churches was published on pro-Islamic State websites, CNN said.

The FBI did not immediately respond to a request for comment.

Islamic State sympathizers "continue aspirational calls for attacks on holiday gatherings, including targeting churches," CNN quoted the bulletin as saying. The notice describes different signs of suspicious activity for which police should be alert, it said.