Greece, Cyprus and Israel have rejected a Turkey-Libya maritime deal that Libya's eastern-based parliament ratified last month, saying it violates the rights of other countries and has no legal effect.
The three countries also agreed to look at jointly developing and producing military equipment.
Senior defense officials from the three countries met in Athens.
In a joint statement, they said the 2019 memorandum between Turkey and Libya "violates the sovereign rights of third states" and ignores international rules on maritime boundaries. Libya's House of Representatives ratified the deal on Oct. 20.
Greece says the agreement draws Turkish and Libyan maritime zones across waters it considers its own, south of the island of Crete. It has also clashed with Turkey over an electricity cable planned to link Greece and Cyprus.
Without naming Turkey, the three countries opposed "unilateral claims, coercion, threats of the use of force and destabilizing military buildup."
They said no country in the region should be used as a "springboard" for actions that threaten regional security.
They reaffirmed their support for the sovereignty and territorial integrity of Cyprus, which has been split since a 1974 Turkish invasion that followed a coup aimed at union with Greece.
The officials discussed forming a working group to link their defense industries and pursue joint development, production and technology projects.
They also focused on protecting shipping lanes, energy routes and undersea infrastructure.
The meeting builds on a summit of the three countries' leaders in Jerusalem in December 2025. The three have grown closer over the past decade through energy and security cooperation.