Riot police stormed a leftist citadel in Germany's second-largest city, Hamburg, to arrest 13 suspects after stones had been thrown at police officers on patrol earlier on Sunday.
Hamburg police detained 13 people at the Rote Flora
The battered building, the Rote Flora, has been the scene of friction between radicals and the authorities down the years and was a headquarters for rioters just before the G8 summit in Germany a year ago.
Police said the conflict began when a night patrol detained a leftist for using tear-gas during an early-morning scuffle. Other leftists freed the man and pelted a police car with stones. A policewoman was cut by breaking glass.
Determined to make an arrest, police sent 370 riot officers, a helicopter and several water cannon. They cut open the doors and searched the building, detaining the 13 holed up inside.
Some 250 leftists outside jeered at "the forces of repression" and promised demonstrations against the "police excesses."