Twenty-five people have been arrested in raids across Germany on suspicion of plotting to overthrow the government.
The group of far-right and ex-military figures are said to have prepared to storm the parliament building, the Reichstag, and seize power.
A minor aristocrat described as Prince Heinrich XIII, 71, is alleged to have been central to their plans.
According to federal prosecutors, he is one of two alleged ringleaders among those arrested across 11 German states.
The plotters are said to include members of the extremist Reichsbürger [Citizens of the Reich] movement, which has long been in the sights of German police over violent attacks and racist conspiracy theories. They also refuse to recognise the modern German state.
Other suspects came from the QAnon movement who believe their country is in the hands of a "deep state".
Plotters prepared to kill for their ends
An estimated 50 men and women are alleged to have been part of the group, said to have plotted to overthrow the republic and replace it with a new state modelled on the Germany of 1871 - an empire called the Second Reich.
"We don't yet have a name for this group," said a spokeswoman for the federal prosecutor's office.
Three thousand officers took part in 130 raids across much of the country, with two people arrested in Austria and Italy. Those detained were due to be questioned later in the day
Justice Minister Marco Buschmann tweeted that a major anti-terror operation was taking place and a suspected "armed attack on constitutional bodies was planned".
The federal prosecutor's office said the group had been plotting a violent coup since November 2021 and members of its central "Rat" (council) had since held regular meetings.
They had already established plans to rule Germany with departments covering health, justice and foreign affairs, the prosecutor said. Members understood they could only realise their goals by "military means and violence against state representatives", which included carrying out killings.
Investigators are thought to have got wind of the group when they uncovered a kidnap plot last April involving a gang who called themselves United Patriots.
They too were part of the Reichsbürger scene and had allegedly planned to abduct Health Minister Karl Lauterbach while also creating "civil war conditions" to bring about an end to Germany's democracy.
A former far-right AfD member of the lower house of parliament, the Bundestag, is suspected of being part of the plot, and of being lined up as the group's justice minister. Birgit Malsack-Winkemann, who was among the 25 people arrested, returned to her role as judge last year and a court has since turned down attempts to dislodge her.
A prominent lawyer was pencilled in to handle the group's foreign affairs, with Prince Heinrich as leader.
Aristocrat 'fuelled by conspiracy theories'
Heinrich XIII comes from an old noble family known as the House of Reuss, which ruled over parts of the modern eastern state of Thuringia until 1918. All the male members of the family were given the name Heinrich as well as a number.
Descendants still own a few castles and Heinrich himself is said to have a hunting lodge at Bad Lobenstein in Thuringia.
The rest of the family have long distanced themselves from the minor aristocrat, with one spokesman telling local broadcaster MDR during the summer that Heinrich was an "at times confused" man who had fallen for "misconceptions fuelled by conspiracy theories".
As well as a shadow government, the plotters allegedly had plans for a military arm run by a second ringleader identified as Rüdiger von P.
They were made up of active and former members of the military, officials believe, and included ex-elite soldiers from special units. The aim of the military arm was to eliminate democratic bodies at local level, prosecutors said.
Rüdiger von P is suspected of trying to recruit police officers in northern Germany and of having an eye on army barracks too. Bases in the states of Hesse, Baden-Württemberg and Bavaria were all inspected for possible use after the government was overthrown, officials said.
One of those under investigation had been a member of the Special Commando Forces, and police searched his home and his room at the Graf-Zeppelin military base in Calw, south-west of Stuttgart.
Another suspect has been identified as Vitalia B, a Russian woman who was asked to approach Moscow on Heinrich's behalf. The Russian embassy in Berlin said in a statement that it did not "maintain contacts with representatives of terrorist groups and other illegal entities".
Several violent attacks have been linked to Germany's far-right in recent years. In 2020, a 43-year-old man shot dead nine people of foreign origin in the western town of Hanau, and a Reichsbürger member was jailed for killing a policeman in 2016.
The Reichsbürger movement is estimated to have as many as 21,000 followers, of whom around 5% are considered to belong to the extreme right.