Thousands of police carried out raids across the country in connection with the suspected far-right ring - ITV Security News Security Rohit Kachroo reports
Federal prosecutors said some 3,000 officers conducted searches at 130 sites in 11 of Germany's 16 states.
The searches were against members of the so-called 'Reich Citizens' movement - some of its members reject Germany's postwar constitution and have called for the removal of the state leadership.
Justice Minister Marco Buschmann described the raids as an "anti-terrorism operation", adding that the suspects may have planned an armed attack on institutions of the state.
Prosecutors said 22 German citizens were detained on suspicion of "membership in a terrorist organisation".
Meanwhile, three other people, including a Russian citizen, are suspected of supporting the movement.
German media outlet Der Spiegel reported that among the locations searched by police were the barracks of Germany's special forces unit KSK, in the southwestern town Calw.
In the past, the unit has been scrutinised over alleged far-right involvement by some soldiers, however federal prosecutors declined to confirm or deny that the barracks was searched.
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Along with the arrests in Germany, prosecutors said that one person was detained in the Austrian town of Kitzbuehel and another in the Italian city of Perugia.
Those detained are alleged to have last year formed a "terrorist organisation with the goal of overturning the existing state order in Germany and replace it with their own form of state, which was already in the course of being founded".
Prosecutors added that the suspects were aware that their aim could only be achieved by military means and with force.
They are alleged to have believed in a "conglomerate of conspiracy theories consisting of narratives from the so-called Reich Citizens as well as QAnon ideology".
Members of the group have also been accused of believing Germany is ruled by a so-called 'deep state'.
Similar baseless claims about the United States were made by former president Donald Trump.
Heinrich XIII P. R. and Ruediger v. P. were identified by prosecutors as the suspected ringleaders, in line with German privacy rules.
Der Spiegel reported that the former was a well-known 71-year-old member of a minor German noble family, while the latter was a 69-year-old former paratrooper.
Federal prosecutors said Heinrich XIII P. R. - whom the group planned to install as Germany's new leader - had contacted Russian officials with the aim of negotiating a new order in the country, once the German government was overthrown.
He was allegedly assisted in this by a Russian woman, named as Vitalia B.