Police swooped on 12 homes and other sites in six states "as part of a federal investigation on suspicion of forming a right-wing extremist organisation", the prosecutor's office said in a statement.
Six suspects, "connected primarily via social media", are accused of founding the group "and in early 2016 beginning plans for armed attacks against police officers as representatives of the state, asylum seekers and members of the Jewish community".
Another seven people are believed to have offered assistance to the group including acquiring weapons.
"There is not as yet any evidence of specific attack plans."
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Around 200 police officers took part in the coordinated raids.
The prosecutor's office in the southwestern city of Karlsruhe declined to provide further details.
But news agency DPA said the group was believed to belong to the "Reichsbuerger" (Citizens of the Reich) movement, a shadowy far-right outfit blamed for shooting dead one police officer and wounding three others during a raid in the southern town of Georgensgmuend in October.
The 41-year-old gunman was seriously wounded and three police officers suffered light injuries.
The Reichsbuerger group does not recognise the legitimacy of the German republic and believes in the continued existence of the German empire or "Reich".
As a result, many members refuse to pay taxes and fines owed to the state. Authorities believe the movement has several thousand members.
A report today in Berlin's daily Tagesspiegel newspaper citing security sources said that the number of far-right extremists in Germany believed to be violent had increased to 12,100 last year, up from 11,800 the previous year.