German prosecutors have filed terrorism charges against 27 people, including a self-styled prince and a former far-right lawmaker, in connection with an alleged plot to topple the government that came to light with a slew of arrests a year ago.

An indictment against 10 suspects, including the most prominent figures, was filed on Monday at the state court in Frankfurt. Under the German legal system, the court must decide whether and when the case will go to trial.

Nine of the suspects, all German nationals, are accused of belonging to a terrorist organisation that was founded in July 2021 with the aim of “doing away by force with the existing state order in Germany”, federal prosecutors said in a statement.

Prosecutors said the accused believed in a “conglomerate of conspiracy myths”, including Reich Citizens and QAnon ideology, and were convinced Germany was ruled by a so-called “deep state”.

Adherents of the Reichsbürger, or Reich Citizens movement, reject Germany’s postwar constitution and have called for bringing down the government, while QAnon is a global conspiracy theory with roots in the US.

The nine suspects are also charged with “preparation of high treasonous undertaking”. They include Heinrich XIII Prince Reuss, whom the group allegedly planned to install as Germany’s provisional new leader; Birgit Malsack-Winkemann, a judge and former lawmaker with the far-right Alternative for Germany party; and a retired paratrooper.

The group planned to storm the parliament building in Berlin and arrest lawmakers, prosecutors said. It intended to negotiate a post-coup order primarily with Russia, as one of the allied victors of the second world war.

They said Reuss tried to contact Russian officials in 2022 to win Russia’s support for the plan. It is not clear how Russia responded.

A Russian woman identified only as Vitalia B is accused of supporting the terrorist organisation, in part by allegedly setting up a contact with the Russian consulate in Leipzig and accompanying Reuss there.

A further 17 alleged members of the group were charged in separate indictments at courts in Stuttgart and Munich, prosecutors said.

Officials have warned repeatedly that far-right extremists pose the biggest threat to Germany’s domestic security. This threat was highlighted by the killing of a regional politician and an attempted attack on a synagogue in 2019. A year later, far-right extremists taking part in a protest against the country’s pandemic restrictions tried and failed to storm parliament.

In a separate case, five people went on trial in May over an alleged plot by a group calling itself United Patriots – which prosecutors say is also linked to the Reich Citizens scene – to launch a far-right coup and kidnap Germany’s health minister.