A German folk festival in Schorndorf in Baden-Württemberg was rocked this weekend by riots and a number of sexual assaults by men police describe as coming from migration backgrounds.

On Saturday night, police arrested three 17-year-old asylum seekers from Afghanistan who are accused of sexually harassing several women at the festival. The night before several other sex attacks were reported, both at the festival and in nearby fields with one Iraqi man identified as a suspect, Die Welt reports.

On the final night of the festival on Sunday police say that around a thousand young people gathered in the town centre, where they rioted and rampaged. Police say that close to 50 percent of the rioters came from a migrant background.

The riot is reported to have started after someone threw a glass bottle, but police say they have no idea who threw it. The initial incident led to people throwing glass bottles at the facade of the Schorndorf Castle and at the police.

The violence did not stop with glass bottles, and during the course of the night several gangs of young men numbering 30 to 50 people roamed through the town centre armed with knives.

Police spokesman Ronald Krötz said, “the violence against the officials was frightening, ” and blamed the large consumption of alcohol for the violence. Police did arrest one German man but shortly released him after questioning. Authorities say the exact number of crimes committed over the weekend is still unknown.

Migrant sex attacks at German festivals are not a new phenomenon. Last year in Bremen there were 24 cases of sexual assault during a multi-day cultural festival and all five suspects in the case were migrants from Afghanistan.

One witness at the festival said the attacks were widespread saying, “I would say definitely more than half of the women who were at this show and stood toward the far front, were touched by these types. I would say definitely, 30 women.”

There were more sex attacks several months later at a festival in Essen. Police arrested several migrant men after witnesses described sex attacks similar to the ones which occurred in Cologne on New Year’s Eve in 2015.

Music festivals have also become targets for radical Islamic terrorism as well, after a Syrian asylum seeker attempted to enter a festival in July of last year. The asylum seeker was denied entrance to the Bavarian event and instead chose to blow himself up near a restaurant killing himself and wounding a dozen others.