Greece has vowed to take "all appropriate measures" to defend its sovereign rights after Libya's parliament ratified a contested maritime boundary deal with Turkey.
The move reopens one of the eastern Mediterranean's most combustible disputes and hands Ankara a significant diplomatic win.
"Geography and the international law of the sea cannot be changed by unilateral, legally unfounded parliamentary decisions," Greece's Foreign Ministry said in a sharply worded statement.
The vote by Libya's eastern-based House of Representatives marks a striking reversal.
The chamber had long opposed the 2019 memorandum, which Turkey signed with Libya's rival government in Tripoli.
Its endorsement now gives the deal a broader stamp of Libyan approval, and it signals Ankara's growing influence in a part of the country once seen as firmly outside its orbit.
Athens insists the ratification changes nothing.
The ministry called the pact "illegal, invalid and null," arguing that it breaches the U.N. Convention on the Law of the Sea.
It also said Turkey and Libya share no opposite or adjacent coastlines that could justify such a boundary. The deal, it said, simply erases Greek islands, including Crete, and their right to maritime zones.
Greece said it had briefed its partners and allies and urged Libya to avoid steps that could destabilize the region.
The European Union moved swiftly to back Athens.
In a joint statement, European Commission President Ursula von der Leyen and European Council President Antonio Costa declared the agreement "null and void" and reaffirmed the bloc's solidarity with Greece and Cyprus. Cyprus also condemned the vote.
The timing is pointed. Greece is preparing to resume seabed surveys next month for the Great Sea Interconnector, a European Union-backed undersea power cable linking Greece and Cyprus. Turkey has invoked the Libya memorandum to claim that the route crosses waters it considers its own. In July 2024, Turkish warships shadowed a survey vessel near the Greek island of Kasos, stalling the work.
With Libyan lawmakers now behind the deal, Ankara has fresh grounds to press its claims. When the survey ship returns to sea, the dispute will move from paper to water.