German Chancellor Angela Merkel told Turkey to stop invoking Berlin's Nazi past in criticising cancellations of Turkish ministers' rallies in Germany, and said she would do everything possible to keep Turkish domestic conflicts from spilling onto German soil.
Turkish President Tayyip Erdogan, who survived an army attempt to topple him last July, is working to win the votes of Turks abroad in an April referendum that would give him sweeping new powers. But unease is spreading in Europe over the dispatch of ministers to communities themselves sometimes deeply divided.
"To the many people with Turkish roots who are German citizens or have lived here for a long time, I say: you are part of our country," Mrs Merkel said yesterday.
"We want to do everything we can to make sure that possible internal Turkish conflicts are not carried over into this life together (here).
"Let us support our way of life together and even improve it where possible. That is a matter of the heart."
Some took a harsher line than Mrs Merkel.
Andreas Scheuer, head of her CSU Bavarian sister party, said "the campaigner Erdogan and his henchmen" were not wanted in Germany.
The dispute over cancellations has become entangled with other tensions between Turkey and its Nato allies.
West European politicians have accused Mr Erdogan of using the coup as a pretext for mass arrests and dismissals that stifle dissent. Mr Erdogan, for his part, accuses European powers of racism, harbouring enemies of Turkey, including Kurdish militants, hardline leftists and people linked to the coup. Scores of Turks, including diplomats and army officers, have applied for political asylum in Germany, Switzerland, Greece, and other countries.
Mrs Merkel spoke unusually bluntly in the Bundestag lower house of parliament, calling for the release of a German-Turkish journalist being held in a Turkish prison. She said she was saddened by deep differences between the allies.
Mr Erdogan's references to Germany's Nazi past were, however, "so misplaced that you can't seriously comment on them". "These comparisons of Germany with Nazism must stop. They are unworthy of the close ties between Germany and Turkey and of our peoples," she said.
Turkey's foreign minister effectively repeated the comparison within hours.
"We are not calling the government Nazi. Its practices recall that era," NTV television quoted Mevlut Cavusoglu as saying.