More than a dozen police officers in the German city of Stuttgart were injured on Saturday evening after a check for drugs sparked vandalism against local shops and police cars.
Police said in a statement that the violence in Stuttgart, in the south-western state of Baden-Wurttemberg, started after officers conducted a drugs check in the city centre during the night between Saturday and Sunday.
Groups then started attacking shops, police officers and patrol cars with "large stones and other objects, including paving stones". Several instances of looting were also reported.
"In order to hide their identity, the perpetrators deliberately covered themselves with balaclavas and other materials," police said.
Some 200 officers from the Stuttgart area had to be deployed, police said, adding that "nineteen police officers were injured".
At least 30 shops, including mobile phone shops, clothing stores and jewellers have been damaged by rioters. Eight were the victims of looting.
"In addition, the perpetrators also damaged billboards and added graffiti," police said. Twelve patrol cars were also partially damaged.
Twenty-four suspected rioters have been detained and are currently being questioned. Police are also reviewing footage circulating on social media and have asked witnesses to forward them any further evidence.