Germany threatens to put Turkey on 'travel black list' following new arrests of nationals

Turkish authorities are believed to have arrested another two German citizens, Germany's foreign ministry said on Monday, with Berlin saying that a travel warning could be issued if detention of nationals continues.

The fresh arrests come amid a new flare-up between the two countries over various issues, including Turkey's detention of several German citizens.

Foreign Ministry Spokesman Martin Schaefer told reporters that Berlin had "specific indications" that a married German couple had been taken into Turkish custody over the weekend.

The reason for the pair's arrest is unknown, however, Schaefer added that one of the couple was released and told to leave Turkey.

"That means the nightmare of so many German nationals who wanted nothing else than to have a holiday in Turkey continues," he said.

"It can affect anyone who decides to travel to Turkey. You expect no danger and suddenly you're in a Turkish prison - that is the sad reality we are confronted with."

The spokesman said that faced with such "capriciousness" from Turkey, Germany may reconsider placing Turkey on its travel blacklist.

"If it becomes daily routine for the Turkish authorities to detain German citizens at the border and put them in police custody... then it is possible that the moment will have arrived that a travel advisory will be issued," he said.

"Then Turkey would join a list of countries such as Libya, Yemen and Syria in which no one would think of going on holiday."

Relations between Berlin and Ankara have been hugely strained since Turkey's failed coup in July last year. Germany has been strongly critical of President Recep Tayyip Erdogan's crackdown on suspected coup supporters, which has included the arrests of over 50,000 people.

Relations soured further when several German citizens, including Die Welt correspondent Deniz Yucel, were detained. 

Turkey currently holds 11 German citizens, according to Germany's foreign minister.

In a sign of how far relations have deteriorated, German Chancellor Angela Merkel recently announced her intention to speak with her EU counterparts to call off membership talks with Turkey.