"It takes two to tango," German Foreign Minister Sigmar Gabriel says, "we can't go on as before" | Sean Gallup/Getty Images Relations with Turkey ‘can’t go on as before,’ says Germany Berlin issues travel alert following arrest of German human rights activist.

BERLIN — Germany issued a travel alert for Turkey on Thursday, citing "heightened danger" after the arrest of a German human rights campaigner in Istanbul and marking the latest in a string of incidents that have pushed tensions between Berlin and Ankara close to breaking point.

Foreign Minister Sigmar Gabriel voiced scathing criticism of Turkish President Recep Tayyip Erdoğan at a press conference, saying Ankara had "abandoned the ground of European values" by jailing "innocent visitors to their country on outrageous charges." Gabriel added he believed that Turkey had also abandoned NATO's common values.

Gabriel's comments followed the arrest on July 5 of Peter Steudtner, a human rights activist from Berlin whom Turkish authorities accuse of supporting a terrorist organization. Steudtner was participating in a workshop with Amnesty International in Istanbul when he was taken into custody.

The minister also announced a wider shift in German-Turkish relations, saying the Turkish president had time and again shown he was not interested in engaging in dialogue. "It takes two to tango," he said, adding "we can't go on as before."

Economy Minister Brigitte Zypries struck a similar tone in a statement emailed to POLITICO. “We are experiencing a nadir in German-Turkish economic relations,” she said.

Zypries said that she would “discuss with our European partners how to proceed. This applies to questions of economic aid for Turkey or the further development of the customs union [with the EU].”

Germany has so far trodden softly in its disputes with Ankara, although it remains unclear if Berlin's approach has achieved its intended goals. Following Turkey's decision to ban German parliamentarians from visiting an airbase in Incirlik, Germany decided in June to withdraw its troops.

Germany's stance has been driven, at least in part, by a desire to avoid derailing the refugee deal struck last year with Erdoğan, under which Turkish authorities stop refugees from traveling into Europe and in return European governments provide funding to the government in Ankara.

“Time and again we showed great patience, when there were accusations which at times are unbearable for German ears" -- Sigmar Gabriel

But Gabriel said things had changed. He said the arrest of a German human rights activist proved that "anybody can be affected" by random arrests.

"We therefore have to redefine our policy on Turkey," said Gabriel, who said this was also the view of Chancellor Angela Merkel and her Social Democrat challenger in September's parliamentary election, Martin Schulz.

Gabriel said “enhanced alerts" that had so far been in place for certain professions — such as journalists — that could face danger in Turkey would now be extended to all German citizens. The website of the foreign ministry was updated to warn all Germans of possible arrests.

“Persons traveling to Turkey for private or business reasons are advised to be more cautious and to register, even for short stays, on the crisis list of German consulates," the ministry said.

'We have been disappointed'

Two additional measures that the German government will now discuss on top of the travel alert, according to Gabriel, are a suspension of credit guarantees for businesses that invest in Turkey, and a possible cutting of EU pre-accession aid promised to Turkey as part of its accession process to the EU.

"One cannot recommend anyone invest in a country where ... there are examples of expropriations," Gabriel said.

The minister, a Social Democrat, also said he personally supported the call of his party leader, Schulz, to freeze negotiations on updating the EU's customs union with Turkey.

Gabriel suggested that Germany is running out of patience with Turkey. The government had exercised "a lot of patience, even if that was not easy," when Erdoğan "accused Germany of behaving like Nazi Germany" because it wanted to avoid "tearing down bridges," he said.

"Time and again we showed great patience, when there were accusations which at times are unbearable for German ears. We held back and did not pay back in kind. Time and again we counted on the hope that sanity would prevail ... Time and again, alas, we have been disappointed. Time and again, the next step of escalation was taken," Gabriel said, adding that "the developments in Turkey are obvious and one has to call a spade a spade."

Anyone who had fired judges and jailed journalists, Gabriel said, "apparently wants to turn back the wheel of history and dismantle the ... foundations of rule of law and democracy in Turkey."

The incarceration of the 45-year-old Steudtner added to already tense relations between Germany and Turkey. Gabriel interrupted his vacation on Wednesday to summon Turkey's ambassador. Ankara hit back, saying Germany's criticism of Steudtner's arrest was "a direct interference in matters of Turkey's judiciary," according to Reuters.

Last week, Ankara surprised Berlin by banning German lawmakers from visiting German soldiers stationed at the NATO airbase in Konya, central Turkey.

German tabloid Bild, citing unnamed sources in the German foreign ministry, characterized the current tension as Erdoğan taking German citizens as "hostages" to force Germany to hand over possible supporters of last year's failed military coup who have asked for political asylum in Germany.

Spiegel Online on Thursday reported Erdoğan had offered to release German-Turkish journalist Deniz Yücel in exchange for two former Turkish army generals during a visit by Gabriel in June.

Asked about the reports, Gabriel said he had heard about the offer in the press but had not received any calls or letters over the past weeks offering a swap. "I don't know of an official offer for an exchange," he said.