Turkish President Recep Tayyip Erdogan warned Greece to start a dialogue over who owns the seas around Greek islands or face the wrath of his country's military might as the European Union is trying to find some way to de-escalate the brewing crisis.

"They will understand that Turkey has the political, economic and military strength to tear up immoral maps and documents," he said at a hospital's opening ceremony in Constantinople, said Germany's state broadcaster Deutsche Welle.

Erdogan sent the energy research vessel Oruc Reis and a fleet of warships off the Greek island of Kastellorizo, planning to drill under the guise of a maritime deal with Libya, dividing the seas between them, claiming parts of Greece's Continental Shelf.

Greece countered with its own warships shadowing the Turkish vessels and a seas boundaries deal with Egypt, leading Erdogan to cancel talks planned that time with Greek officials and Ankara.

He had pulled his ships at the time at the behest of German Chancellor Angela Merkel but sent them back after the Greece-Egypt deal as she has stepped into the breach to try to prevent a conflict and shooting war.

"They're either going to understand the language of politics and diplomacy, or in the field with painful experiences," Erdogan said, adding: "As Turkey and the Turkish people, we are ready for every possibility and every consequence."

The Turkish newspaper Cumhuriyet reported that 40 tanks were being transported from the Syrian border to the northwest Turkish city of Edirne and carried photographs of armored vehicles loaded on trucks.

Erdogan's warning came after NATO said military officers from Greece and Turkey had begun technical talks to avoid armed conflict or accidents which proved wrong after Greece denied it.

Both countries belong to NATO but the defense alliance repeatedly refused to intervene over Turkish provocations, including Erdogan sending fighter jets and warships to violate Greek airspace and waters, leading to mock dogfights between pilots.

The European Union, which counts Greece and Cyprus as members, has threatened possible sanctions against Turkey over its "illegal" actions, the news site said, after being reluctant to confront Erdogan.

Bloc leaders were fearful if he were pushed too hard and too far that he would unlesh more refugees and migrants on the EU through Greece during an essentially-suspended 2016 swap deal.

Erdogan said that he would not compromise, reversing his call for talks that he said would be based on Greece making concessions as Prime Minister and New Democracy leader Kyriakos Mitsotakis was building an international alliance against Turkey.

Erdogan said, “Turkey is ready for any kind of sharing (of energy resources) as long as it is fair."  He stressed that Turkey was "ready for every eventuality and result,” with Mitsotakis saying Greece would not negotiate with a gun at its head.