The German Foreign Ministry declined to comment. Turkish officials could not immediately be reached to comment.
The report comes at a time when German Chancellor Angela Merkel is actively seeking closer ties with Turkey, a candidate for European Union membership, whose help she needs in tackling Europe`s migrant crisis.
Merkel led efforts to seal a controversial EU deal with Turkey earlier this month intended to halt illegal migration flows to Europe in return for financial and political rewards for Ankara.
Erdogan has harshly criticized Western diplomats after several showed up on Friday to support Can Dundar, editor-in-chief of the Cumhuriyet newspaper, and his colleague Erdem Gul on the first day of their trial in Istanbul.
Erdogan is known for his sensitivity to criticism. Turkish prosecutors have opened nearly 2,000 cases against people for insulting Erdogan since he became president 18 months ago, the country`s justice minister said this month. They include cartoonists, academics and even schoolchildren.
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