Charges of unlawful assembly and use of uniform in public were brought against 11 members of a group trying to enforce aspects of strict Islamic Sharia law in the North Rhine-Westphalia city, a spokeswoman for the Wuppertal police told The Local.
Officers stopped the 11-man group on the street on Wednesday. Some were wearing orange vests bearing the words 'Shariah Police', in violation of federal German law, the spokeswoman said.
The group has been stopping young people at local drinking and gambling establishments and urging them to abstain from activities deemed to be ungodly according to Islam.
The Wednesday incident was the first time they had directly violated the law, and no formal complaints had been made against them.
"There is no evidence that they have intimated anybody," the spokeswoman said, adding that talks were under way between integration authorities and local mosque leaders to address the situation.
"Can a vest and a name really cause such a headache?" the group posted on its page after the encounter with police.
"What have all the grumblers now coming out of the woodwork done for wayward youth?" it also asked. "Do you realize how many are buying and consuming drugs? If you are so honest and good, where is your shrieking and outrage?"
Don't cross the line, warn police
Meanwhile, the Wuppertal police on Friday released a statement pledging to crack down on anyone seeking to take the law into their own hands, especially with any use of intimidation or force.
"The state has an exclusive monopoly on the use of force," reminded local police chief Birgitta Radermacher. "Any conduct that intimidates, provokes or makes people insecure will not be tolerated. These 'Sharia Police' have no legitimacy," she added.
There had been repeated attempts, especially at night time, by members of the Salafi Islamist community to influence and recruit young people, the statement said.
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Police presence in the city centre had been strengthened and citizens were urged to report sightings of the group, which has said it will expand its activities in other towns.
The group reportedly identifies itself with the Salafi movement, an ultra-conservative sub-group within Islam with a strong following in the Middle East. Most of the world's Salafis are from Qatar, UAE and Saudi Arabia.
"In this way they are demonstrating that they do not recognized our law-based state," an interior ministry spokesperson told the Rheinischer Post newspaper.
The head of the local CDU branch and security expert for the Christian Democrats in the state, Peter Biesenbach, described the situation as an "alarm signal".