Austria and the Netherlands on Monday backed Germany in its latest diplomatic spat with Turkey, saying their governments would follow suit in preventing campaign appearances by Turkish politicians in support of constitutional reform.
"There are four or five European countries that are affected, (but) our solution in Austria is that we do not accept electoral campaign appearances by Turkish politicians," Austrian Foreign Minister Sebastian Kurz said at a meeting of EU foreign ministers in Brussels.
"We principally don't want electoral campaigns from other countries to be carried out in Austria, and conflicts from other countries to shift to Austria," he said.
"I don't think its desirable for ministers who represent the state to hold campaign rallies in the Netherlands," said Dutch Foreign Minister Bert Koenders. "It's important to say this to the Turkish authorities."
Diplomatic ties between Berlin and Ankara have been strained in recent weeks by Turkish plans to lobby its large expatriate population in Germany ahead of the vote, which could approve greater powers for the Turkish presidency. Some 1.4 million Turkish people here are eligible to vote in the referendum.
A decision by local authorities in south-western Germany to withdraw permission for Turkey's justice minister to use a venue for a campaign speech caused the row to escalate, with President Recep Tayyip Erdogan likening the ban to "Nazi practices."
German government representatives condemned those remarks.
"When it comes to the rule of law, tolerance and liberality, Germany is second to none," Peter Altmaier, Merkel's chief of staff, told public broadcaster ARD.
Speaking in Brussels, German Foreign Minister Sigmar Gabriel said the German-Turkish relationship was "very tense" and needed to be normalized.
"Every country has a different position on that and in Germany we have a clear legal position, but I think it's important that everyone tries to establish a normal dialogue again," he said.
By Naveena Kottoor and Friederike Heine
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