President Tayyip Erdogan accused Germany of behaving as in Nazi times in cancelling political meetings of resident Turks that were due to be addressed by Turkish officials.
German authorities withdrew permission last week for two rallies by Turkish residents in German cities amid growing public outrage over Ankara's arrest of a Turkish-German journalist, dragging bilateral ties to a new low.
The planned rallies were part of a Turkish government campaign to win support among Germany's 1.5 million-strong Turkish community for sweeping new presidential powers going to referendum in April. The German authorities cited security concerns.
"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?"
Relations between the two Nato partners have deteriorated sharply since a failed July coup bid against Mr Erdogan, when Ankara accused Berlin and other capitals of failing to condemn rogue military elements quickly or convincingly enough.
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 last 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 was due to attend two events in Germany yesterday, 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.
Julia Klockner, deputy leader of Chancellor Angela Merkel's Christian Democratic Union, said Mr Erdogan was "reacting like a wilful child that cannot have his way".
"The Nazi comparison is a new high point of intemperance," she told the 'Bild' newspaper.
Ms Klockner said Mr Erdogan must apologise for the Nazi comparison. "True statesmen do not speak in such terms."