BERLIN -- Hundreds of German police used antiterrorism laws yesterday to raid the offices and apartments of activists they suspect may disrupt next month's Group of Eight summit with firebombings and other attacks.

Security officials also announced tighter border controls ahead of the June 6-8 summit in the northern resort town of Heiligendamm.

Some 900 federal and local police officers in Berlin and other cities searched about 40 offices and apartments used by left-wing activists and groups opposed to globalization , they said.

Prosecutors said they are investigating more than 18 people suspected of organizing a group that plans to carry out firebombings and other violence to hinder the summit of world leaders.

"The militant extreme left groups and their members are suspected of having founded a terrorist group, or of being members of such an organization, with the specific goal of staging fire bombings and other violent attacks in order to disrupt or prevent the upcoming G-8 summit in Heiligendamm," federal prosecutors said in a statement.

Germany's interior ministry announced it will tighten border controls to screen out violent protesters. People can usually travel freely within the European Union but individual countries maintain the right to tighten checks for security purposes.

Violence has marred past summits, particularly in 2001 in Genoa, Italy, when police and protesters clashed in the streets for days.

Federal prosecutors said the raids focused on dismantling a computer server by which they said many leftist groups maintained websites and mailing lists.

Activists, who will hold approved marches in nearby Rostock ahead of the summit, said the raids were aimed at silencing protests against the G-8, disrupting communication among antiglobalization groups, and tracking down the names of individuals involved in them.

Some groups that were targeted in the raid plan to block roads leading to Heiligendamm on June 6 to prevent politicians, journalists, and service staff from reaching the summit, one activist said.

"The consequences of these searches for us is that it will bring the groups closer together and we will continue to mobilize for a massive blockade of the G-8 summit," said Tim Laumeyer, a member of the Anti-Fascist Leftists of Berlin.

Police took copies of the group's mailing lists and data on their computers. Investigators also searched apartments, a photo archive, left-wing publishing houses, and community centers.

"The goal of the raids was to collect information about potential disruptions during the G-8 and intimidate activists ahead of the summit," said Christoph Kliesing, a lawyer for the protesters.

A member of Gipfelsoli Infogruppe, a group that collects and spreads information about protests against the G-8, said its Web page had been down all day.

© Copyright 2007 Globe Newspaper Company.