Turkish president Recep Tayyip Erdogan has said he will "stir up the world" if he is banned from giving speeches in Germany.
Diplomatic tensions have been rising after German authorities withdrew permission for two rallies in German cities amid growing public outrage over Ankara's arrest of a Turkish-German journalist.
“Now they think Tayyip Erdogan wants to go to Germany. I will go if I want to," Mr Erdogan said at a meeting in Istanbul over the weekend, the Hurriyet daily reports.
"If you don’t let me in, or restrain me from giving a speech, then I will stir up the world."
Mr Erdogan has come under fire for accusing Germany of "Nazi practices" for withdrawing permission for the rallies.
"Germany, you don't have anything to do with democracy," he told a rally in Istanbul. "These current practices of yours are no different than the Nazi practices of the past."
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.
Mr Erdogan also told the meeting: “I am calling out to the German authorities, I am calling out to the world that believes in democracy: If we are fighting for freedom, if we are not uncomfortable with freedom of speech, if we believe in democracy, nobody can block us."
Germany's government condemned Mr Erdogan's Nazi remarks as "absolutely unacceptable."
"Germany cannot be outmatched regarding the rule of law, tolerance and liberalism," Chancellor Angela Merkel's chief of staff told German public Television ARD.
Ms Merkel's spokesman Steffen Seibert said the German government "strongly rejected" the equation of modern Germany with Nazi Germany, adding that such comparisons downplayed the crimes of the Nazis.
Mr Seibert noted there were strong social, economic and military ties between Germany and Turkey, but acknowledged that there were "far-reaching differences of opinion" between Berlin and Ankara at the moment.
Relations between the two NATO partners deteriorated sharply after 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, who has been 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.
Berlin has demanded the release of a German journalist arrested in Turkey last week, whom Mr Erdogan described as a "German agent".
The leader of Germany's Turkish community has accused Mr Erdogan of damaging ties between the two NATO allies with his remarks.
"Erdogan went a step too far. Germany should not sink to his level," Gokay Sofuoglu, chairman of the Turkish Community in Germany, which groups 270 member organisations, told Reuters.
He said the comments could harm bilateral ties and were exacerbating long-simmering tensions within the community of about 3 million people of Turkish background in Germany.
Mr Sofuoglu said he had talked to police after receiving messages accusing him of being a "terrorist" because of his criticism of Mr Erdogan and of a coming referendum to expand the powers of the Turkish presidency.
But he urged authorities not to ban Mr Erdogan or other Turkish politicians from Germany, saying it was important to set a positive example and preserve rights to freedom of expression.
