Turkey has called on Germany for clarification after a confidential government document leaked to the German press referred to the country as a "central platform for action for Islamist groupings".
Turkey's foreign ministry said on Wednesday that the allegations were further "evidence of the biased attitude that, for some time now, attempts to demoralise our country while taking aim at our president and government".
In the statement, the ministry asked for "a clarification from German courts", saying that Turkey was a country that "always fights terror sincerely regardless of the origin".
It also said that the same was expected from Turkey's partners and allies.
Without confirming the contents of the paper, Germany's interior ministry admitted that it made a mistake in transmitting the classified written response to a politician without first consulting the foreign ministry.
In an effort to calm the row, interior ministry spokesman Johannes Dimroth stressed the importance of Turkey in fighting armed groups.
"We are deeply convinced that Turkey is the most important partner with regard to the fight against the so-called Islamic State group," he said.
The foreign ministry, meanwhile, refused to confirm the content of the document that was the response to a question from a Left party politician, which was published by German public broadcaster ARD.
"On what has been published in the media, we do not share the assessment as a whole," said Sawsan Chebli, the spokeswoman of the foreign ministry.
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The official German document, seen by ARD, said the "Islamisation" of Turkey's domestic and foreign policy has made the country a hub for "Islamist" groups.
"As a result of the increasing Islamisation of Ankara's domestic and foreign policy since 2011, Turkey has become a central platform for action for Islamist groupings in the ... Middle East region," said an official response to an inquiry from the opposition Left Party.
According to ARD, the document noted that "the numerous statements of solidarity and action of support for the Egyptian Muslim Brotherhood, Hamas and groups of armed Islamist opposition in Syria by the ruling party AKP and President [Recep Tayyip] Erdogan underline their ideological affinity to the Muslim Brothers".
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The development was the latest blow to the ties between the two countries.
Erdogan singled out Germany for criticism in his speech in early August, after a German court ruled against allowing him to appear on a video link to address a crowd of about 30,000 supporters and anti-coup demonstrators in the German city of Cologne.
He accused Germany and the West in general in supporting the July 15 failed military coup that attempted to unseat him.
"Those we considered friends are siding with coup plotters and terrorists," he said.
He complained that no foreign leader had visited Turkey after the coup attempt, while France and Belgium received visits in solidarity after attacks there.