Police later said no device was found.

It is believed the incident was linked to party leader Sigmar Gabriel’s visit to the town of Heidenau which has been the scene of violent right-wing protests over a refugee centre.

The SPD’s secretary general Yasmin Fahimi said that irrespective of the threat, there had been a flood of racist emails over the past 24 hours, some of them with criminal content which will be reported to the police. It’s thought the bomb threat against Willy-Brandt-Haus is all part of a campaign of hate and violence.

There has been a recent spate of arson attacks across Germany including the burning down of a sports hall in the town of Nauen near Berlin, where some 130 asylum seekers were due to be housed. No one was hurt.

Last weekend’s clashes with police in Heidenau in which 30 officers were injured, underscores how tense the situation across Germany has become as asylum seekers pour in from war-torn countries. More than 800,000 refugees are expected this year alone.

Chancellor Angela Merkel is due to visit the town of Heidenau later today (Aug 26). She will meet asylum seekers, volunteers and security forces.

Survey’s show a majority of Germans welcome the refugees. Hajo Funke, an expert on the far-right at Berlin’s Free University, said the situation was not as bad at it was in the years after the fall of the Berllin Wall, when xenophobic riots broke out and German politicians failed to respond forcefully. “The situation is becoming tense, “he said, “ because of a small group of a few thousand neo-Nazis with violent tendencies.”

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