German police raided Wednesday homes and offices of militant groups who were suspected of plotting attack on the Group of Eight (G8) summit in Heiligendamm, Germany, in June.
Around 900 police and prosecutors have searched 40 premises in six states including Berlin, Hamburg and Bremen, said an e-mail statement from the office of the Federal Chief Prosecutor.
"The suspects in this probe allegedly belong to a group which is planning to obstruct the G8 summit with violent actions and bomb attacks," it said.
Prosecutors said they have identified 18 people so far in one group, which had claimed responsibility under different names for 15 bombings or other vandalism in Hamburg and Berlin.
The G8 summit on June 6-8 will attract heads of government from Canada, France, Germany, Italy, Japan, Russia, Britain and the United States.
Other countries that will join the talks include China, Brazil, India, Mexico and South Africa.
Also on Wednesday, Germany announced that it was reimposing border checks on a case-by-case basis for the next few weeks in order to stop potential offenders to enter Germany to protest during the summit.