Twelve Germans are being held as political prisoners in Turkey, according to Berlin, with the latest two arrests announced Friday.
Relations between Berlin and Ankara have been in a downward spiral since last summer, when a failed coup against Turkish President Recep Tayyip Erdoğan sparked a crackdown on civil liberties and mass arrests of the political opposition, activists and journalists, including German citizens.
Germany has accused Erdogan of attempting to silence his critics at home and abroad. Erdogan, in turn, has called on voters in Germany to reject the country's biggest parties in next month's election.
Steffen Seibert, Merkel's spokesman, warned that Germany expects "German citizens who are imprisoned for incomprehensible reasons, be released."
According to Germany's Foreign Ministry, its consul in Izmir was informed by nongovernmental authorities of the latest arrests and hasn't been able to make contact with the two yet.
Speaking at her annual summer news conference this week, Merkel said Turkey's jailing of Germans was further damaging already fraught ties between the two countries.
"We must see how things develop, but we are calling now, very clearly, for the release of those who are imprisoned," she said.
"Several German citizens are being held in prison, which we believe is not justified. We therefore decided to take a new direction in our policy toward Turkey."
German-Turkish journalist Deniz Yucel, right, has been imprisoned for 200 days, German authorities say.
Deniz Yucel, a German-Turkish journalist, was arrested in Turkey in February on charges of terror propaganda. He has been held for 200 days, according to German authorities.
Dogan Akhanli, who lives in Cologne, was released after a court hearing on the condition he remain in Madrid, according to his attorney.
Akhanli's arrest prompted German government accusations that Turkey is using Interpol, an international police organization, to hunt down Erdogan's political opponents abroad.
Germany threatens trade and travel restrictions
Germany has changed its tactics over Turkey in recent months, threatening to impose travel and trade restrictions if journalist Yucel and activist Steudtner aren't released from prison.
Last month, German Foreign Minister Sigmar Gabriel warned Germans against traveling to Turkey and suggested that the German government would review corporate investments in Turkey.
"Someone who detains law-abiding visitors to their country on the basis of outlandish, indeed absurd, accusations and throws them into prison has left European values behind," Gabriel said in July, calling for Steudtner's release. "We cannot continue as before."
A few weeks earlier, Turkey's Foreign Ministry criticized an art installation in Berlin depicting Erdogan as a dictator that coincided with the G20 summit in Hamburg, calling it "a new example of rising racism and xenophobia in the country."
Soon after, the Turkish government blocked German lawmakers from visiting German troops stationed in Turkey participating in NATO operations in Syria.
Earlier this year, German officials prevented top politicians, including Erdogan, from addressing Turkish rallies in Germany in the lead-up to an April referendum that handed Erdogan sweeping new powers.
In response, Erdogan likened the German government to that of Adolf Hitler. "I thought that Nazism was over in Germany, but it turns out that it is still going on," he said. "It is still going on, it is clear."
Merkel warns Erdogan over election
Relations with Turkey are a key issue in the run-up to Germany's federal elections, and some 3 million people with Turkish roots live in Germany.
Germans go the polls September 24, with Merkel widely expected to secure a