Turkey issued a travel warning against Germany in a tit-for-tat move following a similar warning from Germany against Turkey
Turkish government warnings to its citizens in Germany to be "cautious" and avoid political gatherings during election season are a "bad joke," Chancellor Angela Merkel's most senior aide said on Sunday.
"Turkey's travel warning against Germany is a bad joke!" Peter Altmaier, head of Merkel's chancellery office, wrote on Twitter.
"Imprisonment without charge for many Germans is unjust! Nazi comparisons offend our honour!" he added, referencing two bones of contention in a long-running Berlin-Ankara spat.
Ties have plummeted since last year's attempted overthrow of President Recep Tayyip Erdogan and Germany's strong criticism of an ensuing crackdown which saw more than 50,000 people arrested.
Relations further deteriorated after the detention of several German citizens, including Deniz Yucel, a correspondent for the Die Welt newspaper.
In July, Germany updated foreign ministry travel advice to warn citizens that they could face arrest if they travel to Turkey, prompting an immediate angry response from Ankara.
"There is a risk of similar detentions in all parts of Turkey, including in tourist regions," the German advice reads.
Imprisonment without charge for many Germans is unjust! Nazi comparisons offend our honour!
- Peter Altmaier, senior aide to Angela Merkel
It falls short of a formal travel warning, issued for war-afflicted countries such as Afghanistan, Iraq or Yemen, which would make obtaining travel insurance harder.
"We can't take [away] from tourists the decision whether to travel or not," Foreign Minister Sigmar Gabriel said.
"But we have described in detail what you should be aware of before you go."
In a tit-for-tat update to its own travel guidance, Turkey on Saturday warned citizens living in or travelling to Germany "to be cautious, taking into account the situation in Germany where they could risk xenophobic or racist treatment".
Meanwhile, Turkish politicians have not skimped on references to Germany's grim past in attacks on Berlin.
Erdogan himself decried "Nazism" last week, after an election debate in which Merkel and Social Democratic rival Martin Schulz both endorsed ending Turkey's EU accession talks.
"The government in Ankara is losing its sense of proportion," Schulz told news website Spiegel Online Sunday.
"Germany is not a country that can accept every single humiliation from Turkey."