France, Greece, Egypt and Cyprus have condemned deals signed between Turkey and Libya's United Nations-recognised government assigning Ankara rights over a vast area of the eastern Mediterranean.
A statement issued on Wednesday by the foreign ministers of the four countries, after a meeting in Cairo, declared the agreements "null and void" and said they undermined regional stability.
Their Italian counterpart, who also took part in the meeting in Egypt's capital, did not sign the statement.
The two agreements denounced by the four Mediterranean states are a military pact and a maritime deal, signed in late November by the head of Libya's Government of National Accord (GNA), Fayez al-Sarraj, and Turkish President Recep Tayyip Erdogan.
Libya was plunged into chaos after the toppling and killing of former leader Muammar Gaddafi in a 2011 NATO-backed uprising. In recent years the country has had two governments - the GNA, based in the capital, Tripoli, and a rival administration based in the east.
Ankara is a key ally of the GNA in its fight against renegade military commander Khalifa Haftar, whose forces are aligned with the eastern administration and are backed by Saudi Arabia, Egypt and the United Arab Emirates.
Ankara says the maritime deal aims to protect its rights under international law, and that it is open to signing similar deals with other states on the basis of "fair sharing" of resources.
Erdogan said recently that Turkey and Libya could carry out joint exploration operations in the eastern Mediterranean as per the agreement that awards Turkey exploration rights in a gas-rich area of the Mediterranean, where Greece, Cyprus and Egypt also have interests.
He added that the two sides could work with international companies to search for oil and gas.
But tensions are already running high between the three and Turkey, because of Turkish gas exploration in the eastern Mediterranean off the coast of the island of Cyprus, which is divided between an internationally-recognised government in the south and a rival leadership in the north, recognised only by Ankara.
Turkish activities 'illegal'
The maritime agreement "infringes upon the sovereign rights of third states, does not comply with the law of the sea" and does not have legal enforceability, the French, Egyptian, Greek and Cypriot ministers said in their statement.
The ministers "reiterated the necessity of full respect of the sovereignty and the sovereign rights of all states in their maritime zones in the Mediterranean".
They condemned Turkey's drilling in the exclusive economic zone and territorial waters off Cyprus, calling on Ankara to "immediately cease all illegal exploration activities".
Tensions escalated in Libya in April last year when Haftar launched an offensive to capture Tripoli.
Erdogan also said earlier this week that his country began deploying troops in a non-fighting capacity to Libya to back the GNA in line with the military agreement signed between Ankara and al-Sarraj's government.
He said Turkey's objective was "not to fight", but "to support the legitimate government and avoid a humanitarian tragedy".