Russian President Vladimir Putin says he is hopeful that an agreement on the legal status of the Caspian Sea can be adopted at the next summit of the sea's five littoral states.
Putin made his comments at the fourth Caspian Sea summit in the Russian city of Astrakhan, where he hosted Turkmen President Gurbanguly Berdymukhammedov, Azerbaijani President Ilham Aliyev, Iranian President Hassan Rohani, and Kazakh President Nursultan Nazarbaev.
The next summit will be held in Kazakhstan at an undetermined date.
The Astrakhan meeting is the fourth Caspian summit in some 12 years.
At the opening of a meeting between the five presidents, Putin called the Caspian region "an oasis of peace and true good-neighborliness."
But officials from the five countries have been unsuccessfully working for years to reach an agreement on the sea's legal status so that billions of dollars in natural resources can be exploited.
Currently, the treaties on the Caspian's legal status date back to 1921 and 1940 when Iran and the Soviet Union negotiated the terms.
Azerbaijan, Kazakhstan, and Turkmenistan, countries which emerged after the collapse of the Soviet Union, do not feel bound to those agreements.
The key issue is the legal status of the Caspian, whether it is considered to be a lake or a sea.
INFOGRAPHIC: Caspian Discord
If the five were to agree the Caspian was a lake, it would mean under international law they would have to use the "condominium" approach and equally divide the Caspian's resources -- and the profits from those resources.
If the Caspian is defined as a sea, each country would have its own national sector extending from its shore.
Under such a definition, Kazakhstan in particular benefits as it has the longest coastline with the Caspian and is believed to have more than half the Caspian Sea's oil and gas in its sector.
Conversely, if the Caspian is accepted as a sea, Iran would have access to only some 13 percent. It is widely believed the Iranian section of the Caspian contains the least amount of oil and gas, though relatively little exploration has been carried out there.
Azerbaijan, Kazakhstan, and Turkmenistan have moved ahead quickly in finding foreign investors to help them develop what they regard as their national sectors of the Caspian.
The three countries are unlikely to agree to share the resources from their sectors.
On another important topic, the five presidents in Astrakhan warned they will not accept the military presence of non-Caspian countries on the sea.
Leaders of the five countries have been saying for years they wanted to avoid any militarization of the Caspian, while at the same time all five countries have developed their own naval forces for the Caspian.
Russia, easily the strongest naval power in the Caspian Sea, has been pushing an agreement that excludes outside militaries from gaining any foothold there. Iran has also enthusiastically supported this position.
Regarding fishing rights, the Caspian Sea leaders agreed to recognize a 15-nautical mile sovereignty space adjacent to each country's shoreline and the exclusive right for each country to fish an additional 10 nautical miles beyond the 15-mile zone.
Putin is scheduled to meet separately on the sidelines with each of the leaders attending the summit.
He and Nursultan Nazarbaev are also due to meet at a Russian-Kazakh regional forum on September 30 in Atyrau, Kazakhstan.
Previous Caspian Sea summits were held in Turkmenistan in 2002, Iran in 2007, and Azerbaijan in 2010.