ATHENS — Turkey's effort to claim large portions of the eastern Mediterranean as its maritime territory sets up a clash with EU leaders.

Ankara's surprise border-mapping deal with Libya that attempts to fence off parts of the sea that Greece and Cyprus regard as theirs has enraged both countries and entangled the rest of the EU. At a European Council summit that is due to get underway in Brussels on Thursday afternoon, the bloc's leaders are expected to "unequivocally" support the two EU countries, according to draft conclusions circulated ahead of the meeting.

The EU is already in dispute with Turkey over offshore drilling operations off the coast of Cyprus, something the government on the island has denounced as a violation of its sovereignty. The latest move by Turkey, as part of its so-called Blue Homeland push, is seen by Brussels as an illegal sea-grab to claim access to maritime resources that rightfully belong to others.

“We express our solidarity and our support to Greece and Cyprus,” Josep Borrell, the EU’s new chief diplomat, told reporters this week.

Athens was caught by surprise when, in late November, Ankara announced it had signed a deal with one of Libya's feuding governments — this one the U.N.-backed administration — demarcating new maritime boundaries between the two countries. The proposed line between Libya and Turkey runs close to the Greek island of Crete.

Greece said the deal violates the rules governing the law of the sea as Turkey and Libya don't have overlapping sea zones or common boundaries.

The memorandum of understanding was swiftly ratified by the Turkish parliament last week and was filed with the United Nations.

But Turkey's move inflamed already tense relations with the EU.

Greece said the deal violates the rules governing the law of the sea as Turkey and Libya don't have overlapping sea zones or common boundaries. It complained to the U.N. and expelled the Libyan ambassador from Athens. "This agreement was compiled in bad faith," government spokesman Stelios Petsas told reporters.

War of words

Turkish President Recep Tayyip Erdoğan countered in comments to local media that Greece had gone "berserk."

Greek Foreign Minister Nikos Dendias responded by saying Greece won't make any territorial concessions and called Turkey's actions "blackmail."

Wolfango Piccoli, co-president of political-risk consulting firm Teneo Intelligence, said that the dispute serves multiple purposes for Erdoğan. “Turkey is upping the ante for domestic and international reasons,” he said.

The Turkish leader is under pressure at home from former Prime Minister Ahmet Davutoğlu and wants to use Libya as "a temporary distraction," he added. And Ankara also wants to ensure that its voice is heard in the scramble to apportion lucrative gas concessions in the region.

There are broader strategic goals too. Turkey's Blue Homeland policy envisages its sovereignty stretching across half the East Mediterranean. That vision clashes with the exclusive economic zones of Greece and Cyprus. Athens and Ankara have engaged in exploratory talks since 2002 on the delimitation of their portions of the continental shelf. The last round of negotiations took place in 2016, although diplomats said Greece has repeatedly requested a restart of the talks since then.

Turkey isn't waiting, though. It started conducting offshore drilling operations off the coast of Cyprus, something the government on the island has denounced as a violation of its sovereignty. The EU chastised Turkey over those efforts this summer.

"We genuinely want to have good-neighborly relations with Greece” — Turkish ambassador to Athens Burak Özügergin

That's entangled the dispute in the long-running regional conflict over Cyprus. Turkey has occupied the ethnic-Turkish northern half of the island since 1974, and says it is acting to protect the interests of its compatriots who form a government only recognized by Ankara.

The internationally recognized Greek-dominated south of Cyprus — an EU member — rejects that.

Earlier this month, Cypriot President Nicos Anastasiades said Cyprus had petitioned the International Court of Justice in The Hague to safeguard its offshore mineral rights.

"We genuinely want to have good-neighborly relations with Greece,” Turkish Ambassador to Athens Burak Özügergin told POLITICO, but he complained about Greek offshore territorial claims based on the island of Kastellorizo lying off the southern shore of Turkey, saying, "How can this tiny island claim a sea area four thousand times its size in the Mediterranean?"

Recent discoveries have found massive natural gas deposits off the shores of Cyprus, Israel and Egypt, and Turkey wants its companies to take part in any gas bonanza. Energy Minister Fatih Donmez said Turkey will issue drilling permits for the Mediterranean following the deal with Libya.

Hunting for allies

But Greece isn't giving in. Prime Minister Kyriakos Mitsotakis said, “We have the means and the will to defend our rights. The entire international community is on Greece’s side and rejects the Turkey-Libya pact."

The U.S. State Department called the deal “unhelpful” and “provocative," and Israel and Russia both back Greece.

So far EU countries are lining up behind their fellow members.

The draft Council conclusions seen by POLITICO say the Libyan-Turkish deal "infringes upon the sovereign rights of third States, does not comply with the Law of the Sea and cannot produce any legal consequences for third States."

The U.S. State Department called the deal “unhelpful” and “provocative," and Israel and Russia both back Greece.

But Turkey said it doesn't feel diplomatically isolated. “Quite the contrary, the only problem that our leadership faces is to find time to accommodate the diplomatic traffic,” said Özügergin. “Don’t believe in the smoke-and-mirror tricks that are being used by those who are not happy by the Turkish persistence on protecting its rights, as well as those of the Turkish Cypriots.”

He added that the "EU is not a relevant actor in this matter ... It is not advisable to offer opinions that could complicate matters."

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