Germany said Thursday it had rejected a request by Turkish President Recep Tayyip Erdogan to address ethnic Turks next week in a rally on the sidelines of a G20 summit in Hamburg, sparking an angry response.
The refusal adds to already frosty relations, which have deteriorated badly over Turkey's mass crackdown after a failed coup last year and a host of other rights controversies.
German Foreign Minister Sigmar Gabriel said Berlin had received a request for Erdogan to be able to address members of the three-million-strong Turkish diaspora in the EU country.
"I explained weeks ago to my Turkish colleagues that we don't think that would be a good idea," Gabriel said during a Russia visit, pointing at stretched police resources around the July 7-8 G20 meeting.
"I also said quite frankly that such an appearance would not be appropriate given the current adversarial situation with Turkey," he added, stressing that Erdogan would however be "received with honours".
Erdogan's spokesman Ibrahim Kalin responded by saying the move to prevent the president meeting with Turks in Germany was "incompatible with relations based on friendship and alliance".
"We emphasise that centuries-long German-Turkish relations should not be sacrificed for the sake of short-term electoral calculations," he added, pointing to the upcoming German elections on September 24.
The Turkish foreign ministry said in a statement that "it is regrettable that German politicians make unacceptable remarks motivated it seems by political calculations".
The spokesman of the ruling Justice and Development Party (AKP) led by Erdogan said there was "nothing more natural" than the president meeting Turks in Germany.
"The attitude of Germany is unacceptable," AKP spokesman Mahir Unal told NTV television, adding that Foreign Minister Mevlut Cavusoglu would continue contacts on the issue.
Gabriel said he could "understand" his Social Democratic Party's chancellor-candidate Martin Schulz, who had said "foreign politicians who abuse our values must not be allowed to give inflammatory speeches in Germany".
"I don't want Mr Erdogan, who is jailing members of the opposition and journalists in Turkey, to hold large-scale events in Germany," Schulz told the Bild newspaper.
Directly criticising Schulz, the Turkish foreign ministry said the comments by the former president of the EU parliament showed the "true face of the mentality that we are confronted with".
Erdogan last addressed Turkish-Germans in May 2015, in the city of Karlsruhe. The large Turkish diaspora is a legacy of Germany's massive post-war "guest worker" programme of the 1960s and 1970s.
Tensions worsened further over the campaign for the April 16 referendum on expanding Erdogan's powers, where Germany and other EU states blocked attempts by figures in his ruling party to hold rallies abroad.
Erdogan, who won the referendum, accused the government of Chancellor Angela Merkel of behaviour reminiscent of the Nazis, prompting condemnation in Germany.
Presidential spokesman Kalin in his statement urged Germany "not to repeat the dreadful mistakes of the referendum campaign".
Adding to the tensions, Turkey imprisoned Deniz Yucel, a German-Turkish journalist with Die Welt daily, on terror charges earlier this year.
And this month Germany decided to withdraw its troops who support the fight against the Islamic State group in Syria from NATO partner Turkey's Incirlik base and move them to Jordan after German lawmakers were refused the right to visit the base.