Egypt, Cyprus, and Greece are condemning an "unlawful and unacceptable" bid by Turkey to drill inside waters where Cyprus has exclusive economic rights.
President Abdel-Fattah el-Sissi hosted a meeting Tuesday with Cypriot President Nicos Anastasiades and Greek Prime Minister Kyriakos Mitsotakis in Cairo.
It's the most recent summit between the three countries' leaders aimed at forming an energy-based alliance in the east Mediterranean.
"Turkey's unacceptable practices and drilling … are a blatant assault on the rights of the Cypriot Republic and the international law," Anastasiades told a joint news conference.
He said that Cyprus would resort to "all available diplomatic means to halt Turkey's aggression."
El-Sissi said unilateral practices by Turkey risk destabilizing the whole eastern Mediterranean and "damage the interests" of its countries.
Turkey dispatched vessels to drill for hydrocarbons inside Cyprus' exclusive economic zone, claiming it is protecting its own interests and those of Turkish Cypriots.
It is also at odds with Egypt over boundaries in the east Mediterranean.
Cyprus was divided in 1974 when Turkey invaded after a coup by supporters of union with Greece. Only Turkey recognizes a Turkish Cypriot declaration of independence in the island's northern third.
The Greek Cypriot-led government has said its offshore drilling operations are an exercise of a sovereign right and that any future gas proceeds would be shared equitably if a deal to reunify the island is reached with the breakaway Turkish Cypriots.
The three leaders also condemned Turkey's planned military offensive into northeastern Syria, after President Donald Trump said earlier this week the US would step aside for an expected Turkish attack on Syrian Kurdish fighters, who have fought alongside Americans for years.
They vowed to step up efforts to tackle illegal migration across the eastern Mediterranean and hone their anti-terrorism tactics.
The Greek leader said that Egypt is a strategic partner for the European Union and that Cyprus and Greece would work to strengthen EU-Egypt relations.
In a previous meeting, the three countries agreed to broaden "strategic cooperation" on energy, including how to transport newly found gas in the region to Europe and linking the electricity grids of Europe and North Africa via an undersea cable.
The 2,000 megawatt cable, known as the EuroAfrica Interconnector, will stretch nearly 1,000 miles from Greece to Egypt through Cyprus.