"We need to be clearer than we have been until now so those responsible in Ankara understand that such policies are not without consequences", Gabriel said.
The German government summoned Turkey's ambassador on Wednesday to demand the release of a jailed trainer of human rights activists, and said the foreign minister was interrupting his vacation for consultations on relations with Ankara.
According to the Turkish government, Fethullah Gulen and his network orchestrated the failed coup of July 15, 2016, which killed 249 people and injured 2,000 others.
Relations between Turkey and Germany started worsening past year when the German parliament unanimously passed a resolution calling the killings of Armenians in the Ottoman Empire "genocide".
But as Erdogan has cracked down on dissent, jailed over 100,000 and consolidated power in the year since a failed coup attempt, Germany has been a prime target of his wrath.
In a statement published on Thursday, Turkey's foreign ministry said it has kept Germany's chargé d'affaires in Ankara informed of Steudtner's case, adding, "the independent Turkish judiciary must be trusted".
For his part, Ibrahim Kalin, Turkey's presidential spokesman, accused Germany of "great political irresponsibility" in stepping up its travel warning.
"The situation in Turkey is not transparent and we should call a spade a spade", he said. It said Turkey was Germany's No. 15 export destination and No. 16 source of imports previous year. "As long as you don't, Turkey will perceive Germany as a country which is protecting terrorists".
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The Indian foreign ministry said that both the countries are capable of resolving the issue through diplomatic channels. It said Indian government didn't desire to negotiate a peaceful settlement on the border issue.
German politicians and media have accused Erdogan of detaining German citizens as "hostages" to trade for Turks in Germany, but Gabriel said he "had heard of no official exchange offer".
Gabriel returned to Berlin early from holiday after Turkey arrested six human rights activists, including German Peter Steudtner and the head of Amnesty International in Turkey, on terror-related allegations.
A Turkish court on Tuesday ordered six human rights activists to remain in custody for allegedly aiding a "terror" group - among them Amnesty International's Turkey director Idil Eser and Berlin-based activist Peter Steudtner.
"We believe these statements are a domestic investment in the approaching German elections".
"Until now there was guidance for certain groups but we're saying that now applies to all German citizens, not just for those with certain jobs".
"If respectable German companies are suddenly put on "black lists" and branded as supporters of terrorism then this amounts to a climate that makes new business and investments in Turkey extremely hard", Zypries said.
Turkey accuses Gulen of masterminding the coup attempt, a charge he denies.
The German government declined to comment on the report. "They should know that those threats and blackmails will not find correspondence in Turkey", he said, adding that threats over cancelling Customs Union talks and funds did not comply with the standards of worldwide relations. By contrast, Turkish exports to Germany of some $14 billion made it the No. 1 destination for foreign sales, ahead of the U.K., Italy then Iraq.