WASHINGTON (AP) — Federal authorities are warning Americans that Islamic State sympathizers are continuing to call for attacks on churches and other holiday gathering sites. The warning was issued after a publicly available list of U.S. churches was posted on a militants' social media site.

The FBI and the Department of Homeland Security issued the warning to law enforcement agencies nationwide Friday, just days after an attack at a Christmas market in Berlin. Islamic State militants claimed responsibility for Monday's attack in which a truck plowed into the holiday market, killing 12 people and injuring 56.

FBI spokesman Andrew Ames says the FBI is aware of the list of churches posted online and is investigating its credibility.