A police officer was shot and injured on Wednesday during raids carried out against a far-right group in Germany.
He was hit in the arm while investigating an alleged coup plot.
A man identified as Markus L has been arrested on suspicion of attempted murder.
MPs said the shooting exposed the threat posed by the Reichsbuerger, or Reich Citizens, whose members claim allegiance to the German Reich of 1871 to 1945.
The suspected gunman “rejects the constitutional order” of Germany's post-war democracy, prosecutors said.
“Militant Reichsbuerger are united by hatred for democracy, our state and people who defend our community. We are not dealing with harmless oddballs,” said Interior Minister Nancy Faeser.
Ministers said 20 properties were searched on Wednesday, with some raids taking place across the border in Switzerland.
Markus L was considered a potential witness to the alleged coup plot uncovered in December involving minor aristocrat Prince Heinrich XIII.
A tactical police unit searched Markus L's home in Reutlingen, south-western Germany, prosecutors said.
During the search, he pulled out a high-calibre gun and exchanged fire with police in his living room, leading to the officer being hit. The policeman's condition was unknown.
Benjamin Strasser, a secretary for justice, said the raids followed months of investigations and hit the “biggest terrorist Reichsbuerger cell” uncovered to date.
“The fact that a police officer has apparently been shot shows once again the dangers of operations in this area,” he said.
December raids over 'far-right coup plot' in Germany — in pictures
A police officer was killed in another Reichsbuerger-related raid in 2016.
The group’s activities have led to calls to tighten Germany’s gun laws.
Some extremists are known to be members of recreational shooting clubs.
Experts say the Reichsbuerger grew in influence by latching on to coronavirus-related protests.
The suspected plotters are said to have brought together a wide range of right-wing ideologies and conspiracy theories.
Prince Heinrich XIII was one of 25 people arrested in December in one of the biggest anti-terror raids in German history.
In a separate case, five people were charged with treason in January for allegedly plotting to kidnap Health Minister Karl Lauterbach and unleash “civil war-like” conditions in Germany.
Authorities linked both cases to Reichsbuerger theories that the modern German state is illegitimate.
