Authorities in northern Germany say about 150 police officers have been injured during violent clashes with hundreds of masked demonstrators protesting next week's summit of the Group of Eight leading industrialized nations.
Protesters in the Baltic port city of Rostock threw rocks, bottles and Molotov cocktails at riot police, who used water cannon and tear gas to disperse them.
Officials say 25 police suffered serious injuries. There is no word on how many protesters were injured, but 17 were arrested.
The violence broke out after tens of thousands of peaceful protesters staged a series of marches earlier Saturday.
The activists want the G-8 nations to take more action to reduce poverty, inequality, environmental destruction and restrictions on immigration.
Rostock, part of the former East Germany, is about 20 kilometers from Heiligendamm, the seacoast report where G-8 leaders will begin their three-day summit on Wednesday.
The Group of Eight includes Britain, Canada, France, Germany, Italy, Japan, the United States and Russia.