This Halloween will probably be different from previous years: Clowns have made headlines for weeks now but not in a good sense. Now there are fears in Europe and the United States that things could get much worse this weekend.

On Friday, the German Interior Ministry made the issue a priority, with Interior Minister Thomas de Maiziere announcing a “zero tolerance” policy. Speaking to Chemnitz-based newspaper Freie Presse, de Maiziere said only a swift reaction by authorities would prevent imitators.

“This has nothing to do with harmless Halloween activities, anymore,” de Maiziere said, indicating that police officials would be on high alert over the coming days, in particular.

After spreading in the United States, sightings of creepy clowns have been on the rise in Europe, where the phenomenon is new and researchers as well as authorities are struggling to find an appropriate response.

Europeans often associate Halloween with American traditions, but it dates back to an ancient Celtic festival.

“Scaring others has a long tradition, especially during Halloween,” German psychologist and threat management expert Jens Hoffmann told the Die Welt newspaper. “But this has now gotten out of control; there is a major bandwagon effect.”

According to an analysis by Die Welt, there have been at least 30 attacks, robberies or assaults by offenders in clown costumes over the past weeks in Germany. Similar increases in incidents were registered in other parts of Europe, including in the United Kingdom.

Some bars in the U.K. have announced that they will exclude customers wearing clown costumes on Halloween, and more police officers than usual will be sent on patrol Saturday night as a preventive measure.