"Everyone can be affected".
Germany on Thursday announced it was considering pulling back from investments in Turkey as part of a range of steps in response to Ankara's refusal to address concerns about the imprisonment of a German human rights activist.
On July 12, Germany advised its nationals in Turkey not to openly criticise the government.
Ibrahim Kalin made the comment at a news conference after the Pentagon said on Wednesday that the story put American forces in danger and that the United States had complained to Turkey, a North Atlantic Treaty Organisation ally. In a press conference in Berlin, he said, "We have to be clearer than before, so the authorities in Ankara understand that their policies are not without consequences." .
Relations between Germany and Turkey are increasingly strained.
Turkey and Germany have been locked in a number of diplomatic disputes, including Turkey's way of handling the aftermath of a failed coup in July a year ago, which has sparked massive criticism in Germany. The minister also accused Germany of "embracing terrorists" despite being an ally.More news: Ann Coulter Exchanges Major Shade with Airline Over Seat Relocation Drama
Gabriel's warnings to private as well as business travellers could deal a blow to Turkey's tourism industry. It said Turkey was Germany's No. 15 export destination and No. 16 source of imports a year ago.
The list, forwarded to Germany several weeks ago, names the vehicle maker Daimler and chemical company BASF as backers of terrorism, but also includes a Turkish fast food restaurant and a late-night food store. Accusing Turkey of "departing the basis of European values", the top diplomat also vowed economic retaliation.
The foreign ministry had issued a separate statement calling for the rapid release of the six activists.
The travel sector contributes some US$30 billion (S$41 billion) to the economy in a normal year.
Gabriel said he could not advise companies to invest in a country without legal certainty where "even completely innocent companies are judged as being close to terrorists".
"I can't see how we as the German government can continue to guarantee corporate investments in Turkey if there is the threat of arbitrary expropriation for political reasons". "We think it is important to review aid in light of the latest developments".More news: Brussels threatens Poland sanctions, unprecedented for its judicial reforms
His remarks came after opposition parties increased pressure on the government ahead of elections in September, seeking a harsher tone against Turkey, particularly due to the recent arrests of a number of German citizens for alleged support for terrorist organizations.
The German government declined to comment on the report.
Council of Europe's Secretary General Thorbjorn Jagland said Thursday he told Turkey's Binali Yildirim that "human rights defenders should be able to fulfil their activities freely without being subject to arbitrary interferences by the authorities".
Germany was Turkey's top export destination in 2016, buying $14 billion worth of Turkish exports, according to International Monetary Fund direction of trade statistics. Only China, at $25.4 billion, exported more to Turkey.
Gabriel said Germany would review state guarantees for foreign investment in Turkey and urge businesses not to put their money there, and also reconsider its support for billions in European Union financial flows earmarked over coming years for the long-time aspirant to membership of the bloc.More news: Active search underway for triple shooting suspect in Gardendale