Turkey has expressed anger at perceived slights from Berlin, including a parliamentary motion referring to the 20th century killing of Armenians as "genocide" and the decision by several German cities to ban events at which Turkish officials wanted to campaign for an upcoming referendum on constitutional reform in Turkey.
German Chancellor Angela Merkel, left, and the Prime Minister of Japan, Shinzo Abe, right, attend the presentation of a robot serving sushi during a walkabout at the IT trade fair CeBIT in Hanover, Germany, Monday, March 20, 2017.
"President Erdogan, you are jeopardising everything that you, with others, have built", he said, adding he would welcome "credible signs" to ease the situation.
Tensions broke out in early March after a number of European Union states, especially Germany and the Netherlands, prevented Turkish ministers from attending campaign rallies in their countries.
Merkel's spokeswoman Ulrike Demmer said today: "The government is watching this very closely, and we maintain that Nazi comparisons are unacceptable in any form".
Relations between Turkey and Europe have been severely strained since Turkish ministers were thwarted from campaigning on the continent for a "yes" vote in next month's referendum on expanding Erdogan's powers.
UK seeks to reassure Gibraltar in Brexit talks
But he pointed out that, once the United Kingdom leaves the Union, "there is a difference" compared with the previous situation. In order to remain a part of the EU, Spain offered last autumn to share the sovereignty over the territory.
"We felt a special link to the path that Turkey took (two decades ago), also due to the many people with Turkish roots who live and work and are at home in Germany", he said, adding that that was now at risk. Would this suit the ethics of politics? "Your mission is not to support terrorist organisations, but to extradite them".
Josef Schuster, president of the Central Council of Jews in Germany, said Turkey's Nazi comparisons demeaned the memory of those who perished in the Holocaust and distracted from the real threat of growing anti-Semitism and right-wing populism. "But stop the unspeakable Nazi comparisons".
German Foreign Minister Sigmar Gabriel said he anxious that the conflict would spill over to ties between citizens of German and Turkish descent.
The German government has rejected 11 export requests from Turkey for small arms, munitions and components since November 2016 due to concerns they could be used for "internal repression" or in Turkey's conflict with its Kurdish population, according to answers provided by the economics ministry in response to a query from a left-wing lawmaker.
EU Commissioner Johannes Hahn told the Bild newspaper in an interview published Tuesday that Turkey's prospects for joining the EU would be "increasingly unrealistic" unless it changed course and stopped moving away from European values.
"That is not the way a democratic government treats its citizens", he said.