Police officers work during an anti-terrorism exercise at the police headquarters in Bremen, northern Germany. (Focke Strangmann/European Pressphoto Agency)

The 66-year-old conspiracy theorist and former tour guide was undoubtedly eccentric. He dressed in public like an ancient Druid and occasionally traversed his southern German town by Segway. He accessorized his robe with a wooden spear.

Yet the recent arrest of the German Druid highlights the real-world dangers posed by those propagating a global barrage of online hate. Particularly after the terror attack in London this week that killed four and wounded dozens more, public attention remains focused on Islamist extremism. But in Germany — just as in the United States, where three men from India were recently attacked and Jewish centers and mosques have become the targets of bomb threats — right-wing violence driven by hate is emerging as a far more widespread threat.

On his account on VKontakte — a sort of Russian version of Facebook — Burkhard Bangert raged that he wanted to “annihilate Jews and Muslims.” He shared an image of the Star of David, with text inside calling for the killing of journalists, police officers and bankers.

He also expressed beliefs shared by the “Reichsbürgers” — an expanding movement in Germany with similarities to what are known as sovereign citizens groups in the United States. Its followers reject the legitimacy of the federal government, seeing politicians and bureaucrats as usurpers.

In a January raid, a policeman carries documents out of a house at Wittstocker Strasse in the district of Moabit in Berlin. The effort was part of a nationwide operation against what is known as the Reichsbürger movement. (Paul Zinken/Picture-alliance/dpa/AP Images)

Prosecutors say Bangert’s rage went further than rhetoric. After authorities seized illegal weapons from his home, they charged Bangert and five accomplices with plotting attacks on police officers, Jewish centers and refugee shelters.

“It’s an international phenomenon of people claiming there are conspiracies going on, people with an anti-Semitic worldview who are also against Muslims, immigrants and the federal government,” said Jan Rathje, a project leader at the Amadeu Antonio Foundation, which studies right-wing violence.

“We’ve reached a point where it’s not just talk,” he continued. “This kind of thinking is turning violent.”

Few places are more sensitive to right-wing violence than Germany — a nation where anti-Semitic hate became the driver of the Nazi ideology that eventually led to the Holocaust.

Yet even here, attacks linked to fringe right-wing groups are surging.

Last week, a Munich court found four defendants guilty of forming a far-right terror squad, dubbed the Old School Society, with the intention of bombing refugee centers. Earlier this month, eight Germans went on trial in the eastern city of Dresden for forming a far-right network that allegedly staged five attacks, including the bombing of a left-wing politician’s car and the detonation of explosive devices at two refugee homes.

Preliminary figures for last year show that at least 12,503 crimes were committed by far-right extremists — 914 of which were violent. The worst act: the fatal shooting of a German police officer by a Reichsbürger member. The preliminary figures roughly compare with levels in 2015, but they amount to a leap of nearly 20 percent from 2014.

The last time numbers surged this high, officials say, was in the early 1990s — when Germany recorded a large but short-term jump in neo-Nazi activity following reunification. Authorities say the current surge has been triggered in part by the arrival of nearly 1 million mostly Muslim asylum seekers to Germany. Last year, there were nearly 10 anti-migrant attacks per day, ranging from vandalism to arson and severe beatings.

Yet officials say the rise of ­conspiracy theorist websites, inflammatory fake news and anti-federal government/right-wing activism have thrown more factors into the mix.

In Germany, Bangert was linked to the Reichsbürger movement — a disparate group of nearly 10,000 individuals who reject the authority of federal, state and city governments. Some claim that the last real German government was the Third Reich of Adolf Hitler.

“We see people who are a little mentally disordered, people with economic problems. We see people with conspiracy theories. You also have right-wing extremists, you have esoterics and you have your sovereign citizens. This is the conglomerate of what we call the Reichsbürger” movement, said Heiko Homburg, head of counterextremism at the Brandenburg branch of Germany’s domestic intelligence agency.

While the Reichsbürger movement may be uniquely German, its type of fringe thinking is universal. German intelligence officials describe some of the tools used by members — such as fake passports and the documents used to declare their own governments — as being nearly identical to those used by American sovereign citizens groups.

German officials consider only up to 6 percent of Reichsbürger members to be “right-wing extremists.” Instead, the majority are like Thomas Patzlaff, a 59-year-old Berlin resident who makes a meager income by selling homemade filters because he is convinced that public drinking water is unsafe. Like many in the movement, he does not believe in paying taxes or debts, and almost ended up in prison, he said, after refusing to pay hundreds of euros in parking fines to the Berlin government, which he does not recognize.

He also says he believes he is the reincarnation of Thomas Jefferson — but that’s a whole other story.

“The federal government of Germany does not exist for me,” said Patzlaff, who has written to the pope and foreign embassies to declare his own sovereign state. He defines its borders as his cozy flat in north Berlin — a hub of activity where younger right-wing activists occasionally pop up to seek Patzlaff’s advice.

“I am a German, but the so-called state we live in is just a construct of the elites and the Allies,” Patzlaff said.

Yet officials fear surging membership in such groups is fueling more violence, and German intelligence agencies are now in the midst of compiling a database of armed Reichsbürger members.

In October, a 49-year-old ­Reichsbürger living near Nuremberg, who had declared his home an “independent state,” shot and killed a police officer assigned to seize his hoarded weapons. Last August, Adrian Ursache, 41 — a former “Mr. Germany” — and 13 of his supporters in ­Saxony-Anhalt state tried to prevent his eviction from his “sovereign home” by shooting at police. Police fired back, severely injuring Ursache. Two officers were also hurt.

The violence has left authorities facing the challenging task of separating the truly dangerous from the merely quixotic. Some — like the Druid — authorities say, have crossed a line.

German officials say their January raid of his and 11 other apartments yielded evidence against Bangert and five other people suspected of having formed a far-right extremist network. They are believed, prosecutors say, to have been planning armed attacks against police officers, asylum seekers and Jews.

The local German broadcaster SWR cited police sources as saying that weapons, ammunition, a pen gun and explosives were found in the raids.

Bangert — who used to give tours of the picturesque Rhon Mountains and lived in the southern town of Schwetzingen — has denied the charges and is fighting them. His family insists the charges are trumped up.

“He has always been a bit quirky and done things not everybody would immediately understand,” Friedhelm Bangert, a 63-year-old retired farmer, said of his brother.

“He liked to talk big and had a big mouth, but what he’s accused of, the founding of a terrorist organization . . . from all I’ve heard from his circle of friends, that’s a big joke,” he said.

He said he had last talked to his brother around Christmas, when he confronted him with some of his radical statements.

“He told me, if you don’t overexaggerate, nobody will pay any attention to you,” Bangert said.