The leaders of the five coastal states of the Caspian Sea, rich in resources, signed a historic agreement on their legal status on Sunday in the Kazakh city of Aktau, easing regional tensions and possibly facilitating lucrative oil and gas projects.
The leaders of Azerbaijan, Iran, Kazakhstan, Russia and Turkmenistan signed the agreement on the state of the inland sea, which has been disputed since the collapse of the Soviet Union converted the obsolete agreements between Tehran and Moscow.
The host, Kazakh President Nursultan Nazarbayev, said before the signing that the leaders were "participants in a historic event."
"We can admit that the consensus on the state of the sea was difficult to achieve and not immediate, the talks lasted more than 20 years and demanded a great joint effort from the parties," Nazarbayev said.
Russian leader Vladimir Putin, whose country was seen as the driving force behind the agreement, said the convention was "historically significant" and called for greater military cooperation among the Caspian countries.
The summit on Sunday was the fifth of its kind since 2002, but more than 50 low-level meetings have been held since the Soviet division spawned four new countries on the Caspian coasts.
The agreement somehow solves a long-standing dispute over whether the Caspian is a sea or a lake, which means that it is subject to different international laws.
While the convention refers to the Caspian Sea as a sea, the provisions of the agreement grant it "a special legal status," Russian Deputy Foreign Minister Grigory Karasin told the Kommersant newspaper earlier this week.
The Kremlin has said that the convention holds most of the sea in shared use, but divides the seabed and underground resources.
Iran, which ended up with the smallest part of the sea under the terms of the convention, is seen as a potential loser in the deal.
Iranian President Hassan Rouhani called the convention "an important document" on Sunday, but said it does not end all disagreements over the sea.
"Today we have a framework for actions in the Caspian Sea, which was not the case before," Rouhani said in comments translated into English.
"But there are other issues to deal with in other meetings."
However, Rouhani hailed a stipulation in the convention that prevents non-Caspian countries from deploying military forces at sea.
"The Caspian Sea only belongs to the Caspian Sea states," he said.