PARIS (Reuters) - French police arrested more than 100 people after gangs of masked youths stormed through Paris suburbs and the center of Lyon on Halloween night, authorities said on Thursday, following a message on social media calling for a “purge” against police.

Police fired teargas overnight at hundreds of youths who barged through the city center of Lyon, hassling police and passers by, shattering shop windows and setting rubbish bins on fire.

In the deprived Seine-Saint-Denis area north of Paris, a sportswear store was looted and young people robbing a grocery store attacked police with acid, according to Denis Jacob of police union Alternative Police.

Authorities said the riots were stoked by messages circulated on social media, apparently inspired by the Hollywood horror film franchise “The Purge”, which depicts a violent dystopia in which all crimes are made legal for a day.

“Halloween must remain a celebration, the purge is not a joke, the purge is a threat,” Interior Minister Christophe Castaner told reporters on Thursday.

A young man who wrote a Snapchat message calling for the “purge” against police forces was arrested earlier this week. He was released on Tuesday pending trial on Nov. 28, police said.

Castaner said 15,000 police were deployed all across France on Wednesday night in anticipation, and that violence was less severe than a year ago.

Youths in depressed suburbs of French cities have been torching hundreds of vehicles on New Year’s Eve and Bastille Day since the early 1990s.

Halloween is not traditionally celebrated in France, although it has become more visible since the late 1990s under the influence of American films and TV series, with shop windows often showing hollowed out pumpkin heads and witches.