The U.S. Federal Bureau of Investigation is warning local law enforcement agencies across the United States that Islamic State militants are calling for attacks on churches and other sites where holiday crowds might gather.
The announcement came Friday after the militants posted a list of U.S. churches as possible targets on its social media sites.
"As part of the continuous dialogue with our law enforcement partners," FBI spokesman Andrew Ames said, "the FBI routinely shares information about potential threats to better enable law enforcement to protect the communities they serve."
Ames said citizens are advised to maintain awareness of their surroundings and report suspicious activity.
He added that the FBI "is tracking this matter while we investigate its credibility."
On Monday, Islamic State claimed responsibility for a terror attack on a Berlin Christmas market in which 12 people died and 56 were injured.