“We have assessed this extensive study, which we consider plausible, and that is why I support these decisions by BfV,” Horst Seehofer, the German interior minister, said.
“We both consider this decision wrong,” Alexander Gauland and Alice Weidel, the AfD’s leaders, said in a joint statement, adding that they believed the BfV decision had been the result of “political pressure”.
Ms Weidel went further, claiming that the decision had been the reason for the sacking of the former head of the BfV, Hans-Georg Maassen, last year.
Mr Maassen was removed after he publicly challenged Angela Merkel’s account of riots in Chemnitz last year without providing any evidence to back his version of events.
The decision to classify the Junge Alternative youth organisation and Mr Höcke’s Flügel group as suspected threats mean they can be subject to electronic surveillance and undercover monitoring.
Thomas Haldenwang, the new head of the BfV, described Mr Höcke’s group as “a threat to the liberal democratic principles of the German constitution”.
Mr Höcke has publicly called for a “180-degree turn” in German attitudes of atonement for the Second World War and described the country’s national Holocaust memorial as a “monument of shame”.
Mr Haldenwang said the BfV was also monitoring far-Left groups suspected of being behind attacks on the AfD and could also place them under surveillance.