(CNN)German Chancellor Angela Merkel has demanded the release of German citizens detained in Turkey, describing their imprisonment as "unjustified" on Tuesday.
Merkel warns Turkey over imprisoned German citizens
Relations between Berlin and Ankara have been in a downward spiral since last summer, when a failed coup against Turkish President Recep Tayyip Erdogan 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.
Speaking at her annual summer news conference on Tuesday, Merkel said Turkey's jailing of German citizens 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 towards Turkey."
Deniz Yucel, a German-Turkish journalist, was arrested in Turkey in February on charges of terror propaganda.
In July, Turkish authorities arrested German human rights activist Peter Steudtner and nine others, charging them with "committing crimes in the name of a terrorist organization without being a member."
Earlier this month, a prominent Turkish-German writer who has been critical of Erdogan was detained while on holiday in Spain.
Dogan Akhanli, who lives in Cologne, was released after a court hearing, but on the condition that he remain in Madrid, according to his lawyer.
The incident prompted German government accusations that Turkey is using Interpol, an international police organization, to hunt down Erdogan's political opponents abroad.
Merkel, who spoke for approximately 90 minutes on Tuesday, warned that relations between the two countries were going through a "very complicated" phase.
Merkel said that any desire for improved ties must be based on upholding the principle of rule and law, adding: "We do not see that guaranteed in Turkey at the moment."
Germany has threatened to impose travel and trade restrictions on Turkey if Yucel and Steudtner aren't released from prison. Last month, German Foreign Minister Sigmar Gabriel warned German citizens 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, while calling for Steudtner's release. "We cannot continue as before."
A few weeks earlier, an art installation in Berlin depicting Erdogan as a dictator -- installed to coincide with the G20 summit in Hamburg -- was met with anger by Turkey's Foreign Ministry, which described it as "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 who were 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."
Relations with Turkey are a key issue in the run-up to Germany's federal elections, and some three million people with Turkish roots live in Germany.
Earlier this month, Erdogan called on voters of Turkish origin to boycott the two biggest parties -- Merkel's CDU and the Social Democrats -- along with the Green Party in the election, describing them as "enemies of Turkey," according to CNN affiliate NTV.
The call drew a fierce rebuke at the time from Merkel, who warned Erdogan against interfering in the election.
Germans go the polls on September 24 with Merkel widely expected to secure a fourth term in office.