Diplomats from NATO members Greece and Turkey met in Athens Tuesday to try once more to settle their standoff over eastern Mediterranean borders and energy rights.
Ankara ratcheted up the pressure a notch on Monday with a diplomatic note to Israel, Greece and the European Union, Turkish media reported.
It told them to seek its permission before proceeding with work on a proposed undersea power cable in disputed eastern Mediterranean waters, Turkish state media reported Monday.
Both sides cite a range of decades-old treaties and international agreements to support their conflicting territorial claims.
Hostilities flared last year when Ankara sent a research ship accompanied by a navy flotilla into waters near the Turkish coast that Greece asserts are theirs -- a claim the EU supports.
Those waters are thought to be a possible source of natural gas reserves.
Turkey is furious that Athens is using its web of islands to lay claim to huge swathes of the Aegean and Mediterranean seas.
Tuesday's meeting follows one in Istanbul in January, the first direct talks between the two sides on the dispute in nearly five years -- and which happened only after pressure from the EU.
But the discussion will also be the 62nd such meeting since 2000, a long series that so far has little to show for it.
- 'Provocations' -
Athens has so far only wanted to discuss the border around the Aegean, where some of its islands lie close to the Turkish mainland.
Ankara however insists that the talks should include setting out the exclusive economic zones and air space of the two states.
Little has been released about the agenda for Tuesday's talks, which will take place behind closed doors.
But Turkey knows that at a December EU summit, member states drew up a list of Turkish targets for sanctions over what it said had been Ankara's "unilateral actions and provocations" in the eastern Mediterranean.
A Greek diplomatic source told AFP the bloc's March summit would return to the question. Greece is also counting on the support of US President Joe Biden, the same source said.
On Monday, NATO chief Jens Stoltenberg had also expressed "serious concerns" over Turkey's actions.
"There are serious differences and some issues, ranging from the eastern Mediterranean, the Turkish decision to buy the Russian air defence system S-400 or related to democratic rights in Turkey," Stoltenberg told European Parliament lawmakers.
He added that NATO could be "an important platform for discussing these issues".
Ankara, however, remained defiant Monday.
In a videoconference with military officers, Turkey's Defence Minister Hulusi Akar called on Athens to abandon its "uncompromising and provocative attitudes".
He denounced what he said were Greece's efforts to drag the EU and the United States into what was essentially a bilateral dispute.
"They will not get anywhere like this," he said.