Two German citizens of Turkish origin were arrested in Istanbul over the weekend, the German Foreign Ministry said Monday.

Foreign Ministry spokesperson Martin Schäfer said in Berlin that there were "concrete indications" the married couple had been taken into custody by police in Istanbul on Sunday.

One of the two apparently remains in custody while the second has been released, but barred from leaving Turkey.

Schäfer said there was still no official information on the arrests from Turkish authorities.

Political arrests

The arrests bring the number of German citizens languishing in Turkish prisons to at least 56. At least 12 of those in custody are there for what Berlin says are political reasons.

Late last month another German couple of Turkish origin was arrested in Antalya. The man is still in custody and the woman was released and has since returned to Germany. 

"The nightmare, which so many German nationals who wanted to do nothing other than to spend holiday in Turkey [have experienced] - this nightmare continues," Schäfer said, adding that German nationals who travel to Turkey should be aware of the risk of arrest. 

Among those in custody for political reasons are Die Welt correspondent Deniz Yücel and human rights activist Peter Steudtner. Both face charges related to "terrorism."

Turkish officials have told Germany to "mind its own business" over arrested German nationals. 

Downward spiral

The arrests have raised pressure on Germany to issue a formal travel warning for Turkey, something that Chancellor Angela Merkel has so far rejected. Instead, she has called for blocking talks to expand Turkey's EU customs union deal and implementing other economic measures.   

Relations between Berlin and Ankara started to go downhill after Germany passed an Armenian genocide resolution in 2016, prompting Turkey to retaliate by blocking members of parliament from visiting troops stationed at Incirlik air base. That row ultimately led Germany to pull its troops out of the air base earlier this year and transfer them to Jordan to continue operations against the so-called "Islamic State."

Massive purges and a crackdown on the opposition following the July 2016 failed coup attempt against President Recep Tayyip Erdogan have added to diplomatic tensions. Turkey has arrested some 50,000 people following the failed coup, and more than 100,000 people have been dismissed from their jobs over alleged links to an Islamic movement led by US-based preacher Fethullah Gulen, who Ankara blames for the coup attempt.   

Ankara demands that Berlin crack down on the Gulen movement. Instead, Germany is granting asylum to diplomats, military officers, journalists and others caught up in the crackdown that has raised concerns over the rule of law and democratic backsliding. 

Adding to tensions, German prosecutors are investigating Turkish imams for spying on alleged Gulen followers in Germany. 

In the lead-up to April's constitutional referendum in Turkey granting Erdogan expanded powers, relations hit another low point when the Turkish president accused Germany and other European countries of "Nazi-like" practices for blocking Turkish ministers from campaigning.

Relations with Turkey have also become a political football ahead of national elections in Germany on September 24.

cw/kms (AFP, dpa, Reuters)