BERLIN: Two more German citizens are believed to have been arrested in Turkey, the foreign ministry in Berlin said Monday, adding that a travel warning could follow if the detentions continue, reports AFP.

Foreign ministry spokesman Martin Schaefer told reporters it had "specific indications" that the two Germans, a married couple, had been taken into police custody over the weekend.

It is not known what the pair were arrested for, but Schaefer added one has apparently been 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."

Schaefer said that in the face of such "capriciousness" by the Turkish authorities, Germany would have to consider putting Turkey on its travel blacklist in future.