MOSCOW >> The five countries with shorelines on the Caspian Sea agreed today to a formula for dividing up the world’s largest inland body of water and its potentially vast oil and gas resources.

The leaders of Russia, Iran, Kazakhstan, Azerbaijan and Turkmenistan signed the Convention on the Legal Status of the Caspian Sea, which the Kremlin said in a statement “reflected a balance of interests” of the seashore nations.

Landlocked and less salty than the ocean, the Caspian Sea was regarded by Iran and the Soviet Union — until the Soviet collapse — as a lake, with a border neatly dividing the two countries’ territories.

But when new seaside nations emerged, they sought either their own zones of Caspian territory or a new approach to governing the sea that would classify it as international water with territorial zones and neutral areas, though it has no outlet to the world’s oceans.

The pact signed at a summit in Kazakhstan today takes both approaches in a compromise treating the surface as international water and dividing the seabed into territorial zones.

Iran’s president, Hassan Rouhani, told reporters, however, that dividing the seabed and its mineral wealth would require additional agreements.

Russia, the sea’s main naval power, had opposed splitting the Caspian into national territories that would have confined its own navy to a northwestern corner. The country has launched missiles from its Caspian Sea fleet to strike targets in Syria, flies over the sea to reach Syria, and analysts say, never had the intention of surrendering its military dominance.

The agreement says no country without Caspian shoreline can deploy military vessels in the sea.

In addition, Russia has for much of the post-Soviet period objected to east-west energy trade through subsea pipelines, hoping to keep in place the north-south trade routes of the Soviet Union’s rail and pipeline system.

Oil companies in the 1990s first proposed trans-Caspian pipelines to bring landlocked Central Asia’s energy to market, but that dropped off their agenda as the sea’s legal status was bogged down in talks for decades.

Sunday’s agreement potentially opens the sea for underwater oil and natural gas pipelines, which Russia had opposed, ostensibly on environmental grounds, though it has built such pipes in the Black and Baltic seas.

Only nations whose seabed territories are crossed by the pipelines would have to agree to lay the new pipelines, the convention says, though all five states could have a say on environmental protections. A proposed trans-Caspian oil pipeline could ease exports from the Kashagan oil field in Kazakhstan, which is managed by Exxon.

Starting in the Clinton administration, the United States has pushed for energy, transport and trade across the sea and through Azerbaijan and Georgia, a route known as the Southern Corridor. The diplomatic strategy greased U.S. oil company deals in the Caspian Basin.

An effort in the administration of President George W. Bush to put military might behind the policy by expanding the North Atlantic Treaty Organization to Georgia became a backdrop for a war between Georgia and Russia in 2008, in an indication of the seriousness of Russia’s intent to control the region.

Russia may have agreed to finally resolve the sea’s status now, after three decades of objections, not because of continued Western pressure but because of rising trade competition from China’s “One Belt One Road” policy, according to Shota Utiashvili, a senior fellow at the Rondeli Foundation for Strategic and International Studies in Georgia.

Trade in and out of Central Asia had been diverted not to Russia but to Iran, with Chinese backing, he said. And some Central Asian energy exports have not gone to Russia, but instead east to China because of difficulties exporting west over the Caspian Sea, he added.

Turkmenistan, frustrated in its effort to build a trans-Caspian gas pipeline, has also started work on a pipeline east through Afghanistan to Pakistan and India, known as the TAPI pipeline. The Afghan government has said it could help resolve the war through economic development.

The pipeline passes through Taliban-controlled territory in southern Afghanistan, but it is supported by both the United States and the insurgents as positive for the country’s future.

While the agreement today settled the status of the sea’s surface and created a formula for dividing the subsea resources, the delineation of new borders could prove contentious.

Russia, Kazakhstan and Azerbaijan have divided the seabed in the north, but Iran, Turkmenistan and Azerbaijan have disputed claims to petroleum deposits in the southern portion of the sea. The Caspian basin is seen as an important source of oil for world markets outside the Middle East.