The EU voiced concern on Sept. 5 over what it called "hostile remarks" after Turkish President Recep Tayyip Erdoğan accused Greece of occupying demilitarised islands in the Aegean and said Turkey was ready to "do what is necessary" when the time came.
Historic rivals while also fellow members of NATO, Turkey and Greece have been at odds over issues ranging from overflights and the status of Aegean islands to maritime boundaries and hydrocarbon resources in the Mediterranean, as well as ethnically split Cyprus.
"The continuous hostile remarks by the political leadership of Turkey against Greece...raise serious concerns and fully contradict much needed de-escalation efforts in the Eastern Mediterranean," Peter Stano, spokesman for European Union foreign policy chief Josep Borrell, said in a statement.
"Threats and aggressive rhetoric are unacceptable and need to stop," he added, underlining EU demands that differences be settled peacefully and in full respect of international law.
"The EU reiterates its expectation from Turkey to seriously work on de-escalating tensions in a sustainable way in the interest of regional stability in the Eastern Mediterranean and fully respect the sovereignty and territorial integrity of all EU member states," Stano said.
Ankara has recently accused Athens of arming the demilitarised Aegean islands - something Athens rejects - but Erdogan had not previously accused Greece of occupying them.
Greece reacted by saying it will not follow Turkey in its "outrageous daily slide" of statements and threats.
As Erdogan prepares for what is shaping up to be the biggest electoral challenge of his nearly 20-year rule in 2023, the president has played up achievements in the global stage. He has also stepped up his rhetoric on foreign policy.
Ankara says the Aegean islands were given to Greece under the 1923 and 1947 treaties on condition that it does not arm them. Foreign Minister Mevlut Cavusoglu has repeatedly said Turkey would start questioning Greek sovereignty over the islands if Athens persisted in arming them.