Naturally no-one expects the problems to be solved overnight

Iranian President Mohammad Khatami

"We will need to work on the Caspian for a long time still," he said.

A declaration of general principles was prepared overnight, but the leaders could not agree on it.

Mr Niyazov said each country was trying to defend its own national interests.

The Caspian's oil and gas reserves, thought to be the third largest in the world, have been in limbo since the break-up of the Soviet Union 10 years ago.

American influence

Iran and Turkmenistan want the seabed to be split equally five ways.

Russia and Iran want to limit US influence

But Azerbaijan, Kazakhstan and Russia want the Caspian split into national sectors, corresponding to the length of each country's shoreline.

"What prevailed in our talks was understanding, and that we should solve our problems through understanding. Naturally no-one expects the problems to be solved overnight," said Iranian President Mohammad Khatami.

This was the first time talks on the future of the sea have taken place at presidential level.

The Caspian's natural resources are of growing strategic importance as western countries seek alternatives to oil from the Gulf.

Russia and Iran are keen to avoid a build-up of US influence in the region and held separate, bilateral talks in the Turkmen capital, Ashgabat, on Tuesday.