Berlin - Chancellor Angela Merkel called for calm on Monday in an escalating dispute with Turkey, a day after President Recep Tayyip Erdogan labelled a German ban on rallies by his ministers "Nazi practices".While firmly rejecting Erdogan's claims as "absurd and out of place," Merkel's office sought to draw a line under the dispute that is weighing on already frayed ties."To our Turkish partners, let us talk openly and critically, but let us remember the special meaning of our close relationship and let cool heads prevail," said Merkel's spokesperson Steffen Seibert.Large crowdsSharply rejecting Erdogan's Nazi jibe, Seibert said: "Nazi comparisons are always absurd and out of place, because they lead only to one thing - the trivialising of the crimes against humanity committed by the Nazis."The row erupted late last week after three German local authorities banned the ministers' scheduled appearances ahead of an April referendum over the plan to scrap the prime minister post in Turkey altogether, thereby boosting Erdogan's powers.The German authorities cited capacity problems in hosting the events, which they said were likely to attract large crowds.Merkel has said her government did not have a hand in the decisions, which fell under the jurisdiction of local governments.But Ankara responded with fury to the cancellations, accusing Berlin of working against the referendum.Erdogan told a rally in Istanbul on Sunday: "Germany, you are not even close to democracy. Your practices are not different from the Nazi practices of the past."He also warned Germany not to hinder him from making an appearance if he wished. "If you don't let me in, or if you don't let me speak, I will make the whole world rise up," he said.Voter baseTurkey's Foreign Minister Mevlut Cavusoglu on Monday heaped fire on the attack, accusing Berlin of working to scupper the rallies."The hotels, the conference halls are being put under pressure, police are being sent to the owners of these places: it's systematic pressure, a manoeuvre aimed at erecting systematic barriers," he said.Germany is home to the biggest population of Turkish people abroad, with about three million people of Turkish origin living here, the legacy of a massive "guest worker" programme mainly in the 1960s and 70s.With some 1.4 million Turks in Germany holding the right to vote in Turkey, it is not uncommon to see politicians travelling there from Ankara to seek to sway the significant voter base.