Italian police detained on Wednesday morning an alleged member of the Reich Citizens movement, a far-right group that, according to investigators, allegedly sought to overthrow the German government in an armed coup.
The suspect is a 64-year-old German citizen and was arrested in a hotel in the Ponte San Giovanni area of Perugia.
According to the Italian police, the suspect is a former member of the German army's special corps.
The police reported the suspect will be extradited to Germany as soon as possible.
Wednesday also saw thousands of police officers carry out raids across much of Germany against suspected far-right extremists.
German federal prosecutors said some 3,000 officers conducted searches at 130 sites in 11 of Germany's 16 states. Officials said 25 people were detained.
While police raids against the far right are not uncommon in the country, the scale of the operation was unusual. German media described it as one of the country's largest police actions ever against extremists.
In addition to the raids in Germany and Italy, a suspected far-right extremist was also detained in the Austrian town of Kitzbuehel.
In Berlin, former Bundestag member, Birgit Malsack-Winkemann, was also arrested. Malsack-Winkemann has been a member of the far-right Alternative für Deutschland party since it was formed in 2013
Those arrested are accused of having formed "a terrorist group by the end of November 2021 at the latest, which had set itself the goal of overcoming the existing state order in Germany and replacing it with their own kind of state", a statement read.
The Reichsbuerger movement includes neo-Nazis, conspiracy theorists, and gun enthusiasts who reject the legitimacy of the modern German republic.
Its followers generally believe in the continued existence of the pre-World War I German Reich, or empire, under a monarchy and several groups have declared their own states.
Long dismissed as malcontents and oddballs, the Reichsbuerger has become increasingly radicalised in recent years and is seen as a growing security threat.
They allegedly planned to appoint one of the arrested suspects, identified by local media as an aristocrat and businessman Prince Heinrich XIII Reuss, as Germany's new leader after the coup.
Heinrich XIII had already sought to make contact with Russian officials to discuss Germany's "new state order" after the coup, prosecutors said.
There was, however "no indication that the contact persons responded positively to his request."
A Russian woman named only as Vitalia B., who was among those arrested on Wednesday, is suspected of having facilitated those contacts, prosecutors added.
The Russian embassy in Berlin said it did "not maintain contacts with representatives of terrorist groups or other illegal entities", according to a statement issued via Russian news agencies.