Turkish president Tayyip Erdogan accused Germany on Sunday of "fascist actions" reminiscent of Nazi times in a growing row over the cancellation of political rallies aimed at drumming up support for him among 1.5 million Turkish citizens in Germany.
German politicians reacted with shock and anger. German justice minister Heiko Maas told broadcaster ARD that Mr Erdogan's comments were "absurd, disgraceful and outlandish" and designed to provoke a reaction from Berlin.
But he cautioned against banning Mr Erdogan from visiting Germany or breaking off diplomatic ties, saying that such moves would push Ankara "straight into the arms of (Russian President Vladmir) Putin, which no one wants".
The deputy leader of Chancellor Angela Merkel's Christian Democratic Union (CDU) party said the Turkish president was "reacting like a wilful child that cannot have his way", while a top leader of the CDU's Bavarian sister party described Mr Erdogan as the "despot of the Bosphorus" and demanded an apology.
German authorities withdrew permission last week for two rallies by Turkish citizens in German cities at which Turkish ministers were to urge a "Yes" vote in a referendum next month on granting Mr Erdogan sweeping new presidential powers. Berlin says the rallies were cancelled on security grounds.
However, Turkish economy minister Nihat Zeybekci spoke at large events in Leverkusen and Cologne on Sunday while protesters stood outside.
"Germany, you have no relation whatsoever to democracy and you should know that your current actions are no different to those of the Nazi period," Mr Erdogan said at a rally in Istanbul. "When we say that, they get disturbed. Why are you disturbed?"
The row has further soured relations between the two Nato members amid mounting public outrage in Germany over the arrest in Turkey of Deniz Yucel, a Turkish-German journalist. It has also spurred growing demands for Mrs Merkel to produce a more forceful response to Mr Erdogan's words and actions.
Mr Erdogan, accused by critics of increasingly authoritarian tendencies, has accused Germany of harbouring enemies of Turkey, from Kurdish militants to coup organisers.
He has been sharply criticised in western Europe for mass dismissals and arrests of suspected conspirators, from judges to journalists. Germany has demanded the release of a German journalist arrested in Turkey on Monday whom Mr Erdogan described as a "German agent".
"We will talk about Germany's actions in the international arena and we will put them to shame in the eyes of the world," Mr Erdogan said.
"We don't want to see the Nazi world anymore. We don't want to see their fascist actions. We thought that era was in the past, but apparently it isn't."
Turkish foreign minister Mevlut Cavusoglu on Saturday criticised restrictions on such gatherings in Germany and now the Netherlands as undemocratic, and said Turkey would press on with them in the run-up to the April 16 referendum.
Turkish Economy Minister Nihat Zeybekci plans to attend two events in Germany on Sunday, in Leverkusen and Cologne in the state of North Rhine-Westphalia, which has a large Turkish population.
Germany is Turkey's most important trading partner in the European Union, which Ankara officially aspires to join.
A poll conducted for the Bild am Sonntag newspaper showed that 81 percent of Germans believe that Mrs Merkel's government has been too accommodating with Ankara. Germany, under an agreement signed last year, relies on Turkey to prevent a further flood of migrants from pouring into Europe.