Greece's foreign minister was on a whirlwind tour of eastern Libya, Egypt and Cyprus Sunday amid tensions with Turkey following Ankara's contentious maritime deal with the Tripoli government.
The agreement signed last month expands Turkey's claims over a large gas-rich area of the Mediterranean and has been denounced by Greece, Egypt and Cyprus.
Nikos Dendias met Libya's eastern-based strongman Khalifa Haftar in Benghazi to discuss two recent "unsubstantial" agreements between Turkey and Libya's Tripoli government, according to a Greek foreign ministry statement.
Libya is split between bitterly opposed administrations in the east and west. Since April, forces loyal to Haftar have been fighting to seize the capital Tripoli.
In November, Tripoli's UN-recognised Government of National Accord (GNA) signed the controversial maritime delimitation deal with Ankara, alongside a military cooperation agreement.
Athens says the maritime agreement violates international maritime law and the sovereign rights of Greece and other states, urging the United Nations on December 10 to condemn the deal as "disruptive" to regional peace and stability.
Dendias said Haftar agreed with Greece on the "absolute nullity of these memoranda and how harmful they are" to Libya and regional stability.
Gas at stake
Dendias then flew to Cairo, where he met his Egyptian counterpart Sameh Shoukry for talks aimed at unifying opposition to the maritime deal.
Earlier this month Egyptian President Abdel Fattah al-Sisi denounced Turkey's expansion of ties with the Tripoli-based government.
"We will not allow anyone to control Libya... it is a matter of Egyptian national security," Sisi told reporters, referring to the military cooperation deal struck between Ankara and the GNA.
Dendias was also due to travel to the Cypriot coastal city of Larnaca to meet Cypriot Foreign Minister Nikos Christodoulidis, the island's official news agency reported.
"The condemnation of the Turkish actions is unanimous by all our allies and partners and this is our most powerful diplomatic weapon," Dendias told the Greek weekly Real News on Sunday.
His visits seek to unify opposition to Ankara's moves to expand its control over the continental shelf in the eastern Mediterranean.
Analysts have said Turkey's recent rapprochement with Libya is aimed at preserving access to gas supplies following the recent discovery of vast reserves that has triggered an exploration scramble between adjacent states and international oil companies.
It also comes as energy ministers from Cyprus, Greece, Egypt, Israel, Jordan, Italy and the Palestinian territories agreed earlier this year to create the "East Mediterranean Gas Forum" without Turkey.
"Turkey fears that it is being boxed in from its southern flank, faced with plans for a future gas pipeline to link Cypriot gas fields with European markets," Ege Seckin, analyst at IHS Markit, told AFP earlier this month.
"The maritime boundaries drawn under the deal cover an area that reaches from southwest Turkey to northeast Libya, cutting across the planned route for this pipeline," he said.
Greece is pursuing its own agreements with neighbouring Mediterranean countries, including Egypt and Italy, to delineate their maritime boundaries.
Turkish President Recep Tayyip Erdogan meanwhile vowed on Sunday to increase military support to Libya if necessary.
"We will evaluate all kinds of military support, including ground, marine and air options if necessary," he said.
Although Erdogan has said Turkey is willing to send troops to Libya, the government must seek a separate mandate from the Turkish parliament to send forces to fight there.
In June, Haftar threatened to target Turkish interests in Libya.
On Saturday evening, Haftar's forces announced they had seized a Turkish freighter registered in Grenada off the coast of eastern Libya.