German politicians from across the political spectrum described the "no" in Sunday's referendum on the EU constitution in France as a step backwards and a setback for Germany's attempts to unify Europe.

Guido Westerwelle, the leader of the opposition Free Democratic Party (FDP), said: "This is a setback for Germany's aim to promote the unification of Europe."

Christian Wulff, the Christian Democrat leader of the state of Lower Saxony, said he greeted the news that the French had overwhelmingly rejected the treaty "with great disappointment".

Klaus Wowereit, the mayor of Berlin and a member of Chancellor Gerhard Schroeder's ruling Social Democrats, described the outcome as "a step backwards".

Schroeder himself did not give an immediate reaction.

Germany, which with France forms the key axis at the heart of the European project, last Friday became the ninth country to ratify the constitution.

The treaty was overwhelmingly approved by both houses of the German parliament, but a referendum was not held.