German police have clashed with hundreds of anti-globalisation demonstrators in the northern city of Hamburg, arresting 21 people.
Police reinforcements were deployed to block the protesters
Police used water cannon and baton charges against protesters, who pelted them with bottles and stones.
The violence followed a march by about 4,000 activists angered by what they saw as excessive security for a meeting of EU and Asian foreign ministers.
Germany is also tightening security ahead of next week's G8 summit.
A fence has been erected around the German Baltic Sea resort of Heiligendamm, where the summit will take place on 6-8 June. Protests will be banned from the area of the barrier.