The Berlin authorities have banned a march through the German capital by the far-right National Democratic Party (NPD), planned for Saturday.
The NPD's Holger Apfel won a seat in Saxony
"Anyone who uses incitement to separate people may not demonstrate in Berlin," said the city's interior minister Erhart Koerting.
The NPD picked up 9.2% of the vote in recent state elections in Saxony.
Its mottos for the Berlin march were to be "Berlin must stay German" and "Against Islamic centres in the city".
The NPD's success in Saxony meant it gained seats in a German state assembly for the first time since 1968.
The German government has described the NPD as a latter-day version of Hitler's Nazi Party and tried to ban it last year - a move rejected by the constitutional court.
Chancellor Gerhard Schroeder faces key local council elections in North-Rhine Westphalia on Sunday - Germany's most populous state.