Greece and its EU allies held war games in the Mediterranean on Wednesday while Turkey conducted drills with the US navy nearby as the row between the two neighbours over gas and maritime borders ratched up another notch.
The convergence of a growing number of warships on an energy-rich but disputed patch of the sea between Cyprus and Crete came as NATO and a host of European officials called for cooler heads to prevail.
Greece and Turkey are ancient rivals with a litany of disputes despite both being members of the NATO military alliance.
They nearly went to war over some uninhabited islets in 1996 and had a collision between frigates while Turkey was searching for energy in the east Mediterranean earlier this month.
The threat of another conflict between them could imperil Europe's secure access to a wealth of new energy resources and draw in nations such as Egypt and war-torn Libya.
NATO Secretary General Jens Stoltenberg said he was "personally regularly in contact with Ankara and Athens".
'No concessions'
German Foreign Minister Heiko Maas shuttled between Athens and Greece on Tuesday in a bid to get talks back on track and avoid what he described as a "catastrophe".
But his efforts failed to secure a firm promise from either side to drop their sabre rattling and engage in constructive talks.
President Recep Tayyip Erdogan warned Greece on Wednesday that Turkey would "make no concessions on that which is ours".
Greece was able to secure the support of France -- which became the EU's biggest military power after Britain formally left the bloc -- in three days of war games starting on Wednesday that also include Italy and Cyprus.
The Turkish defence ministry conducted its own drills with an Italian navy vessel on Tuesday.
And the same US destroyer that took part in the exercises with Turkey had staged air and sea manoeuvres with the Greek navy south of Crete on Monday.
The seeming shifts in allegiance highlight Rome and Washington's desire to avoid challenging Erdogan because of Turkey's importance to the conflicts in Libya and the Middle East.
But France has joined Greece in shadowing the Turkish vessels and is openly warning Erdogan against overplaying his hand.
The eastern Mediterranean "should not be a playground for the ambitions of some -- it's a shared asset," French Defence Minister Florence Parly said.
Oruc Reis
Tensions began escalating when Turkey sent the Oruc Reis research vessel accompanied by warships into disputed waters on August 10.
Greece responded by dispatching its own warships to track the Turkish vessels.
But Turkey says this latest conflict really started when Greece struck an exclusion zone agreement with Egypt that conflicted Ankara's maritime claims on August 6.
That pact -- expected to be ratified by the Greek parliament later Wednesday -- was agreed after Turkey delayed the Oruc Reis mission to give diplomacy another chance in July.
Erdogan re-ordered the disputed exploration immediately after the Egypt deal.
Both Athens and Ankara say they would prefer to talk out their problems but are ready to defend their interests with force.
The Greek defence ministry said that "the path of diplomacy remains the preferred means to settle" the dispute.
EU split
Greece is expected to once again push for penalties against Turkey at an informal meeting of EU foreign minister in Berlin on Thursday and Friday.
Turkey has been isolated at such meetings because it is a member of NATO but not the EU bloc.
Its accessions talks to the EU have stalled as Erdogan pushes ahead with a more nationalist and diplomatically aggressive course that plays well to his conservative base at home.
But the EU has refrained from heavily sanctioning Turkey and has only targeted two energy executives for their role in drilling work near Cyprus.
Erdogan has repeatedly used the threat to open Turkey's borders and allow millions of refugees -- many of them from Syria -- to enter EU nations in past disputes.
"If we say we will do something, we will do it, and we will pay the price," he said Wednesday.