RUTHFULLY YOURS

Two events set off the quarrel. One was Turkey’s decision last month to deploy troops to Libya in support of Prime Minister Fayez al-Sarraj and his internationally recognized Government of National Accord, known as the GNA. Then there’s Turkey’s maritime accord with the GNA in November. Egypt has substantial energy interests in the eastern Mediterranean, and the agreement sets out exclusive economic zones for Turkey and Libya that would hamstring further exploration by Egypt in a region rich in natural gas.

There is no shortage of foreign involvement in Libya’s civil war. Egypt—like Russia, the United Arab Emirates and Saudi Arabia—backs Libyan militia leader Khalifa Haftar and the Libyan National Army under his command. Egypt’s President Abdel Fattah Al Sisi has provided logistical support to Mr. Haftar as he fights militias loyal to the GNA. There are reports of more direct support from Egypt, including weapons shipments. Turkey, along with Qatar, backs the GNA, which has ties to the Muslim Brotherhood—an archenemy of Egypt’s secular, military government.

Turkish President Recep Tayyip Erdogan’s decision to deploy soldiers and Syrian fighters to Libya can be understood as a trade for exploration rights off Libyan shores. But it was also a move against the Gulf monarchies that are at odds with Turkey and the Muslim Brotherhood. Mr. Erdogan hopes to resume construction projects worth billions of dollars that have been frozen since Libyan dictator Moammar Gadhafi fell in 2011. He also wants a military foothold in Libya, which will be his entrance into Africa.

Egypt recently made a series of offshore natural-gas discoveries, and exporting resources will help the deeply indebted country. Last year Cyprus, Greece, Israel, Italy, Jordan, Egypt and the Palestinian Authority established the Eastern Mediterranean Gas Forum. The point is to rationalize infrastructure costs, offer competitive prices, improve trade relations and develop energy markets.

Sidelining Turkey from the consortium led to the maritime accord that so angers Egypt. Ankara’s attempt to dictate new boundaries on the sea challenges Egyptian, Greek and Cypriot economic zones. Mr. Erdogan’s regional ambitions include wielding influence in the eastern Mediterranean and asserting Turkey’s “right” to the region’s hydrocarbons. Being left out of the consortium reduces Turkey’s potential share of European energy markets.

Meanwhile, the Turkey-GNA accord would upend a $6.7 billion deal among Israel, Greece, Cyprus and Italy to build an undersea pipeline from the eastern Mediterranean to Europe. At a meeting in Cairo, the foreign ministers of Egypt, France, Greece and Cyprus declared the Turkey-GNA accord “null and void.”

In November, Egypt, Greece and Cyprus conducted joint military exercises to counter “potential threats in the Mediterranean.” In December the Turkish navy intercepted an Israeli research vessel in Cypriot waters. Turkey says it may use military force to uphold the accord. France is sending warships to the area.

Mr. Sisi thinks an Islamist-leaning Libyan government on Egypt’s border could create a haven for global jihadist networks such as ISIS. On Jan. 12, Ali Abdel Aal, Egypt’s speaker of parliament, said Egypt “does not prioritize military solutions over political ones,” but Cairo may resort to military force to thwart Turkey’s “invasion” of Libya. Mr. Haftar has said he could take Tripoli in hours if Mr. Sisi sent him soldiers.

Egypt and Turkey’s diplomatic ties are strained and, with little optimism for a long-term political solution in Libya, there may be more friction and belligerence between them this year. The U.S. needs a clearer vision for Libya, where a sudden frenzy of diplomacy is occurring with America playing only a marginal role. The U.S. also needs a policy for the fierce regional competition under way in the eastern Mediterranean, where a Russo-Turkish axis is forming. If not, America may find it increasingly difficult to pursue its objectives in either area.

Mr. Saidel is a freelance writer and foreign-policy analyst.