German Finance Minister Wolfang Schaeuble on Friday drew parallels between contemporary Turkey and government practices in the former state of East Germany.
"Turkey is arresting people arbitrarily and no longer upholds even minimal standards of diplomatic conduct," Xinhua news agency quoted Schaeuble as saying.
The situation, he said, reminded him of East Germany which was why Berlin could no longer guarantee the safety of German tourists in Turkey, the report said.
"If Turkey does not stop playing these games, we must tell our people: you are travelling at your own risk," Schaeuble said.
After a year of deeply fraught relations between Berlin and Ankara, tensions between the two NATO partners reached boiling point on Tuesday after the Turkish arrest of German human rights activist Peter Steudtner.
The announcement that Steudtner had been placed in police custody sparked outrage in German political circles. The head of the SPD parliamentary faction, Thomas Opperman, complained that Erdogan had inaugurated a "new stage of escalation in German-Turkish relations".
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German Foreign Minister Sigmar Gabriel on Thursday cancelled his holiday to tighten national safety recommendations for travel to Turkey in response to the development.
The Foreign Office officially urged Germans in Turkey to "exercise heightened caution" when in the country.
Gabriel in a strongly-worded speech warned Turkey that Germany would hold talks with the European Union (EU) to re-evaluate financial aid the country currently receives as an accession candidate.
He demanded the immediate release of nine German citizens currently in Turkish police custody.
Turkey is still in official talks to join the EU although new negotiating chapters have not been opened in years. Gabriel questioned whether negotiations over Turkey's customs union with the EU could be completed in the current political climate.
Alongside the Finance Minister, several German politicians expressed support for Gabriel's speech and the resulting toughening of Berlin's stance towards Ankara.
Turkey lashed back at the front of official German criticism, describing Berlin's stance as inappropriate and inacceptable. President Recep Tayyip Erdogan's speaker Ibrahim Kalin said Gabriel's statement was motivated by domestic politics.
A statement from the Turkish Foreign Ministry accused its German counterpart of seeking to benefit from hostility towards Turkey and Turks.
Germany has also frozen existing arms export projects between the two countries as a preliminary measure. While details remaining unclear, such a move would mark an unprecedented step for defence relations between allied NATO partners.
Turkish-German relations have been severely strained since a military coup failed to unseat Erdogan in July 2016.
Ankara has rejected Berlin's criticisms that it engaged in an excessive crackdown on political opponents in response to the coup and is resentful towards its German NATO partner for allegedly granting asylum to Turkish revolutionaries.
There is also a long-standing spat between Berlin and Ankara over attempts to prevent Turkish politicians from holding campaign rallies in Europe.
Hoping to win support amongst Turkish migrant communities for a controversial constitutional referendum which ultimately passed in April 2017, Erdogan and members of his AKP party ran up against heavy opposition in several European capitals.
Turkey retaliated by banning German parliamentarians from visiting their country's armed forces stationed at the Turkish military base of Incirlik and Konya from where they were participating in the international military effort against the Islamic State.
In June, German lawmakers voted to transfer troops from Turkey to a new base in Jordan after several attempts to defuse the diplomatic crisis failed.
--IANS
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