Some of the emails contained bomb and other death treats, or boasted of being in possession of guns and biological weapons, according to revelations by the Süddeutsche daily and NDR regional broadcaster.

The emails were signed either with “National-Socialist Offensive”, a reference to Hitler's Nazi ideology, “Wehrmacht”, the German word for Hitler's army, or “NSU 2.0” — after the NSU neo-Nazi terror cell that murdered 10 people from 2000-2007.

Berlin prosecutors confirmed that they had opened a probe against persons unknown on suspicion of blackmail, incitement and disturbance of the peace.

Among those targeted by the hate mail was German far-left lawmaker Martina Renner who was warned to expect “letter bombs” and “executions of citizens in the street”, media reports said.

Popular German singer Helene Fischer, who last year criticized racist violence at far-right protests in the eastern city of Chemnitz, reportedly also received threats. Her management declined to comment when contacted by news agency DPA.

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Similar emails were sent to court houses in several German cities, as well as the Frankfurt prosecutor's office, Hamburg airport and the tax office in the city of Koblenz.

Other recipients have included the Central Council of Jews, lawyers, journalists and politicians.

“For several months now a group has been sending threatening emails to authorities and institutions across Germany using different sender addresses, without a harmful event occurring,” Koblenz police said in a statement.

“The language in the emails is similar.”

Police have been investigating the emails since last summer, according to DPA.

The most recent emails prompted police to evacuate the main train station in Lübeck on Monday and Gelsenkirchen's tax office on Tuesday, Süddeutsche reported, but no bombs were found.