Berlin-Ankara relations have badly deteriorated amid disputes over Turkey's mass arrests of alleged state enemies since a failed coup last year and a host of other rights issues.
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 7th-8th G20 summit in Hamburg.
"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" at the summit.
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.
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.
But ties have been especially strained since the failed coup in Turkey last July, and tensions have worsened over multiple issues including a referendum campaign to expand Erdogan's powers.
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.