German authorities are increasingly concerned about the radicalisation of a movement that rejects the legitimacy of the federal republic and its constitution, after two violent attacks on police officers within two days.

On Thursday afternoon, a man threw punches at police officers at a town hall office in Salzwedel, Saxony-Anhalt. A day earlier a man in the Bavarian town of Georgensgmünd opened fire on four officers carrying out a raid on his apartment, one of whom has since died of his injuries.

Both men had self-identified as members of the Reichsbürger movement, which does not recognise the laws and institutions of modern Germany but instead adheres to the old German Reich that ceased to exist after the end of the second world war. Many, but not all, of its members are on the extreme right.

The incident in Salzwedel’s town hall escalated after a 43-year-old man with his 34-year-old wife had refused to register their dog, telling the official that he did not recognise modern Germany and its laws as legitimate.

Who are Germany's Reichsbürger? The Reichsbürger movement rejects the legitimacy of the modern Federal German Republic and its institutions, adhering instead to the German Reich with its pre-second world war borders and constitution. The movement is disparate and without a coherent leadership, ranging from far-right ideologues to those who are simply trying to get out of paying their taxes. However, police have in recent months observed a growing tendency towards violence among the movement's followers.

When police arrived after the pair refused to leave the premises, the man started calling the officers “Nazis” and threw punches. During the ensuing altercation, one of the officers dislocated a shoulder and was taken to hospital.

The couple have been temporarily banned from the town hall premises, though are still required to register their dog by post and would be fined if they failed to do so, police said.

During Wednesday’s incident in Bavaria, the Reichsbürger named Wolfgang P opened fire on four police officers through a closed front door as they were ascending the stairs to his first floor flat. Though wearing protective gear and a bullet-proof vest, a 32-year-old officer was hit by three bullets and died of his injuries on Thursday morning.

The 49-year-old financial adviser had come to the attention of local authorities after he had refused to pay motor vehicle tax and removed his name from the local register but had not vacated his apartment.

When notified of a hearing with the antitrust authorities, Wolfgang P had responded with a letter stating: “I am a citizen of the Reich.” According to the newspaper Bild, he had declared his inherited apartment an autonomous state and marked its borders with yellow paint.

The raid on his flat was ordered after P failed to meet a deadline for handing over an arsenal of 31 weapons registered in his name.

The Reichsbürgerbewegung or “Reich citizen movement” is a disparate movement without a centralised leadership. Some of its followers believe in the German Reich with its 1937 borders, including territories now part of Poland, others adhere to the Prussian empire of 1871, while some have even declared their own micro-states.

On 25 August, Adrian Ursache, a former winner of the Mister Germany competition, was injured during a police raid on his parents-in-laws’ premises, which he had declared as an autonomous state called “Ur”. In May 2014, police in Rhineland-Westphalia arrested the self-declared leader of an imaginary state called “Germanitia”.

What unites the various factions of the Reichsbürger movement is a belief that the Weimar constitution of 1919 was never fully abolished by either the National Socialist regime nor the allied forces and therefore remains valid, rendering the Federal Republic of Germany illegal. A phrase frequently employed by Reichsbürger is “BRD GmbH”, stating that modern Germany is merely a “limited company”.

In the past, supporters of the Reichsbürger movement were often regarded as little more than loners and eccentric. But the recent spate of attacks has inspired a rethink among German politicians, with interior minister Thomas de Maiziére asking the country’s internal intelligence agency to revise its current classification of the group.

Bavaria’s interior minister Joachim Herrmann said on Friday that one police officer had this week been suspended for promoting Reichsbürger ideas, while two others were facing disciplinary action.

A police spokesperson in Saxony-Anhalt said there was an “increasing tendency towards physical violence” among members of the movement, but that it was not a phenomenon unique to the state in former East Germany where Thursday’s incident and the raid on Ursache’s flat occurred.

In 2012, a parliamentary question submitted on behalf of the leftwing party Die Linke revealed that at least one member of the Reichsbürger movement was also active in the network around the neo-Nazi National Socialist Underground terrorist group, which was responsible for a series of murders between 2000 and 2006. Back then, the German government estimated the number of the movement’s followers to be in the “lower hundreds”.