Reports in Germany say the group, made up of far-right and ex-military figures planned to storm the parliament building, the Reichstag, and seize power.
Prosecutors say a German man, referred as a prince called Heinrich XIII, 71, was central to the group’s plans.
Federal prosecutors said some 3,000 officers conducted searches at 130 sites in 11 of Germany's 16 states against adherents of the so-called Reich Citizens movement. Some members of the grouping reject Germany's postwar constitution and have called for the overthrow of the government.
Prosecutors said 22 German citizens were detained on suspicion of "membership in a terrorist organization." Three other people, including a Russian citizen, are suspected of supporting the organization, they said.
Weekly Der Spiegel reported that locations searched include the barracks of Germany's special forces unit KSK in the southwestern town of Calw. The unit has in the past been scrutinized over alleged far-right involvement by some soldiers.
Federal prosecutors declined to confirm or deny that the barracks was searched.
Along with detentions in Germany, prosecutors said that one person was detained in the Austrian town of Kitzbuehel and another in the Italian city of Perugia.
Prosecutors said the suspected ringleaders, identified only as Heinrich XIII P. R. and Rüdiger v. P., are accused of last year founding a "terrorist organization 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."
The suspects were aware that their aim could only be achieved by military means and with force, prosecutors said.
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," according to a statement by prosecutors.