German police have raided 50 properties in a series of raids against neo-Nazi group Combat 18.
Politicians have warned of a growing neo-Nazi threat in Germany
More than 300 officers took part in the raids in the northern state of Schleswig-Holstein early on Tuesday.
Police say they found weapons and arrested several people suspected of "forming a politically motivated criminal organisation".
Homes and meeting places used by the group were among the premises targeted.
Combat 18, founded in the UK, takes its name from the position in the alphabet of Adolf Hitler's initials.
The group has been blamed for carrying out or motivating racist attacks.
Tuesday's raids were carried out in the cities of Kiel and Flensburg.
State criminal police spokesman Matthias Hennig said the group has a "hard core" of about 10 members.
German politicians have recently warned that the threat to Germany from neo-Nazis has risen to a new level.
Police believe they foiled a plot to bomb a Munich Jewish centre during a visit by the German president, scheduled for 9 November.
The suspected attack would have coincided with the anniversary of the Nazis' 1938 Kristallnacht attacks, when thousands of Jewish targets were attacked and dozens murdered.