Greek Prime Minister Kyriakos Mitsotakis has demanded tough European sanctions against Turkey to reverse its encroachment on territorial claims across the Mediterranean.
Writing in The Times, Mr Mitsotakis said Europe should stand up as a bloc against Turkey and the "gunboat diplomacy" that has raised tension in the eastern Mediterranean.
"Later this month EU leaders will meet in special session to decide how to respond," he wrote.
"If Turkey refuses to see sense by then, I see no option but for my fellow European leaders to impose meaningful sanctions.
"Because this is no longer just about European solidarity. It is about recognising that vital interests, strategic European interests, are now at stake.
"If Europe wants to exercise true geopolitical power, it simply cannot afford to appease a belligerent Turkey."
At a summit of European states bordering the Mediterranean, Mr Mitsotakis received the backing of French president Emanuel Macron, who said Turkey could no longer be regarded as a regional partner.
"We Europeans need to be clear and firm with the government of president Erdogan, which today is behaving in an unacceptable manner," Mr Macron said.
He said that at the moment, Turkey was "no longer a partner in the region" of the Eastern Mediterranean because of its behaviour, although he hoped to "restart a fruitful dialogue with Turkey."
Mr Macron said Turkey had "intensified provocations in a way that is not worthy of a great state. The Turkish people are a great people and deserve something else".
Unabashed Turkish response
But in a strongly worded reply, the Turkish Foreign Ministry described Mr Macron's comments as "arrogant" and a sign "of his own weakness and despair".
As tension grows, the centre-right bloc in the European Parliament called for a fundamental rethink of ties with Turkey.
"We must end the membership process and rethink a new relationship based on the idea of partnership, in which we are not held hostage," the European People's Party said.
"It is unacceptable for Europe to give in every time [President Recep Tayyip] Erdogan threatens to open Turkey’s borders and break our migration agreements. We have to change the game. We will not be blackmailed."
Greece and Turkey are Nato members but the alliance has struggled to contain the crisis.
Talks were announced by Secretary General Jens Stoltenberg last week at Nato headquarters to try to prevent an escalation from incidents such as a collision between Turkish and Greek warships last month.
The warships were shadowing a Turkish vessel surveying for oil and gas in disputed Mediterranean waters west of Cyprus in an operation that Greece and many other countries condemned as illegal.
Ankara and Athens both view the area as part of their continental shelf.
Greece has said the military discussions rely on the departure of Turkish ships from disputed waters.
