Germany says it would be inappropriate for Turkey's President Recep Tayyip Erdogan to address Turks in Germany during the G20 summit next week.
German Foreign Minister Sigmar Gabriel said Turkey had made such a request officially, but "it's not a good idea".
Turkey was angered by Germany's refusal to let pro-Erdogan politicians address campaign rallies in Germany in March.
Mr Erdogan castigated Germany for the ban, accusing the government of "Nazi-style" behaviour.
Turkish ministers wanted to woo Turkish diaspora voters ahead of the April constitutional referendum, in which Mr Erdogan won sweeping new powers.
Mr Gabriel told German media that "on the sidelines of the G20 we don't have the police numbers to provide the security" necessary for Mr Erdogan to address Turks.
Germany has also warned Turkey not to bring Turkish security agents who were charged for violent scuffles in Washington last month. »