Turkish Prime Minister Binali Yildirim struck a more conciliatory tone earlier Friday, saying that Turkey continues to regard Germany as a "strategic partner in Europe".
"Turkey has started making arbitrary arrests and isn't maintaining the minimum standards for consulates (having access to detainees)", Xinhua quoted Schauble as saying.
Germany's new travel advice set out the problems that have arisen in recent months - nine German citizens are now in custody as a result of the crackdown following last year's coup attempt in Turkey. "You (Germany) do not have the power to smear Turkey. or the power to scare us", he added.
The immediate trigger of Germany's ire was a Turkish court's decision Tuesday to jail Steudtner and the other activists, including Amnesty International's Turkey director and a Swedish IT trainer, who were detained in a July 5 police raid on a hotel on the island of Buyukada, where they were attending a digital security workshop.
"If Turkey doesn't drop these little games, we must say to people: 'You travel to Turkey at your own risk, we can't guarantee anything for you any more, '" he said.
In an unusually hard-hitting statement that swept aside any diplomatic niceties, German Foreign Minister Sigmar Gabriel on Thursday also warned German firms against investment in Turkey and spoke of an "overhaul" of the entire relationship.
Relations between key North Atlantic Treaty Organisation partners Turkey and Germany - already brittle in recent years - have been further eroded in recent days by an intensifying row over the Turkish authorities' recent wave of arrests.
Gabriel stressed that Germany still wanted to rebuild relations with its long-time ally, while urging Erdogan's government "to return to European values".
He demanded the immediate release of nine German citizens now in Turkish police custody.
"These accusations are obviously unfounded and have simply been dragged out irrationally", the foreign minister said, adding that Steudtner had taken no position on current Turkish politics and was quite possibly present in the country for the first time.
A statement from the Turkish Foreign Ministry accused its German counterpart of seeking to benefit from hostility towards Turkey and Turks.
In an interview with Reuters, Zeybekci also denied reports that Turkey gave Berlin a list of companies it was targeting for suspected links to last year's coup attempt. While details remaining unclear, such a move would mark an unprecedented step for defence relations between allied North Atlantic Treaty Organisation partners.
Responding to German criticism over the rights situation in Turkey, Erdogan declared that Turkish courts were "more independent" than German ones.
While one minister in Berlin compared Ankara's behaviour over the detention of six rights activists to the authoritarian former communist East Germany, Turkish President Tayyip Erdogan told Germany to "pull itself together".
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's referendum process in the first part of the year and German parliamentary elections slated to take place on September 24 make the need to find responsible voices to calm down and find a healthy dialogue channel almost impossible.