Greece on Tuesday demanded that Turkey withdraw a research ship at the heart of their growing dispute over maritime rights and warned it would defend its sovereignty, calling for an emergency meeting of EU foreign ministers to resolve the crisis.
Tensions were stoked Monday when Ankara dispatched the research ship Oruc Reis accompanied by Turkish naval vessels off the Greek island of Kastellorizo in the eastern Mediterranean.
In a televised statement, Greek Foreign Minister Nikos Dendias urged Ankara to "immediately" remove the Oruc Reis from Greek waters.
"We call on Turkey to immediately depart from the Greek continental shelf," Dendias said. "We make it clear that Greece will defend its sovereignty."
The incident is the latest spat over energy exploration in the gas-rich eastern Mediterranean, a frequent source of disputes between Turkey and neighbours including Greece, Cyprus and Israel.
On the instructions of Greek Prime Minister Kyriakos Mitsotakis, Dendias said he had asked for an emergency meeting of the European Union foreign affairs council to discuss "Turkey's growing provocation and delinquency".
A spokesman for EU foreign policy chief Josep Borrell said the situation was deeply concerning and needed to be solved through dialogue.
"Apparently the developments on the ground unfortunately show that... more needs to be done in order to defuse the tensions and reverse the very negative and unfortunate trend of escalation," spokesman Peter Stano told reporters.
"That's why (Borrell) stated that he is deploying all efforts necessary to re-establish the dialogue, positive constructive dialogue and to facilitate the re-engagement, and these efforts are ongoing."
Marine tracking on Tuesday located the vessel southeast of the island of Crete. It is escorted by a Turkish navy flotilla and shadowed by Greek warships.
An official Turkish picture shows the Oruc Reis escorted by five warships.
Turkey has announced the vessel would carry out activities between August 10 and 23.
Turkish Foreign Minister Mevlut Cavusoglu said Tuesday his country would step up energy exploration in the eastern Mediterranean and would not "compromise" its rights.
Cavusoglu said Ankara would issue licences for new areas in the "western part of our continental shelf" from the end of August.
"We will conduct all kinds of seismic research, drilling activities. Our determination is absolute," Cavusoglu told reporters.
"We will defend the rights of Turkey... in the eastern Mediterranean and we will not compromise in any way on this," he said.
A similar crisis last month was averted after Turkey pulled the Oruc Reis back to hold talks with Greece and rotating EU chair Germany.
But the mood soured last week after Greece and Egypt signed an agreement to set up an exclusive economic zone in the region.
- 'Antagonism and distrust' -
Mitsotakis on Monday conferred with his military chiefs and spoke with EU Council President Charles Michel and NATO Secretary General Jens Stoltenberg.
Borrell on Sunday called Turkey's actions "extremely worrying" and a recipe for "greater antagonism and distrust".
Turkish President Recep Tayyip Erdogan sounded a slightly more conciliatory note after a meeting with his own ministers later Monday.
"Let us all come together as Mediterranean countries and find a formula that protects all of our rights," Erdogan said in a national address.
But Erdogan added: "We cannot allow (nations) to ignore a big country like Turkey and try to imprison us to our shores."
Stoltenberg urged respect for international law during talks on Monday with the Greek premier.
"The situation must be resolved in a spirit of Allied solidarity and in accordance with international law," Stoltenberg tweeted.
The Turkish foreign ministry has said the Greece-Egypt agreement was "null and void".
Egypt, Cyprus and Greece have likewise denounced a contentious deal, including a security agreement, signed last year between Ankara and the UN-recognised government in Libya.
Greece, Cyprus and Israel in January signed an agreement for a huge pipeline project to transport gas from the eastern Mediterranean to Europe despite Turkey's hostility to the deal.