"The Europeans should hear us, empathise with our suffering and help us. It would be best if they imposed economic sanctions on Turkey," demonstrator Sinan Anin said.
Several hundred police officers were deployed at the demonstration, which police said was peaceful.
On Wednesday Martin Schaefer, spokesman for the Foreign Ministry, said the German government had approved voting by the estimated 1.4 million Turks living in Germany who are eligible to cast ballots in the April 16 referendum. Erdogan is seeking support among Turks abroad for the referendum. German Foreign Minister Sigmar Gabriel has said Erdogan is taking advantage of a sentiment many people of Turkish origin have in Germany that they are neither accepted nor welcomed.
Demonstrator Mustafa Bostan said if Erdogan won the referendum, things would worsen: "It could be that he'll say: 'I've won again' and then he'll start fighting again and destroying Kurdish towns or killing Kurds." Relations between Ankara and Berlin have been burdened by the arrest of a Turkish-German journalist in Turkey and by Erdogan's description of bans on planned rallies by Turkish ministers as "fascist".
Copyright Reuters, 2017