The building of the Caspian pipeline, conceived by the European Union as part of a supply system to reduce EU dependence on Russian gas imports, requires the approval of all Caspian states, Russian President Dmitry Medvedev said on Friday.
The pipeline will be part of a planned corridor of links known as the Southern Corridor.
"This is a rather difficult question, which, of course, directly depends on the status of the Caspian Sea as an inland sea and requires that all the countries which participate in the Caspian summit agree their positions," Medvedev said.
The EU opened talks in September aimed at negotiating a treaty to bring gas from Turkmenistan, with the world's fourth largest reserves, across the Caspian Sea to Azerbaijan and then to Europe in a move Moscow said it regretted.
Russia's Foreign Affairs Ministry said that, under a 2007 politically binding joint declaration of the heads of five Caspian states, only littoral countries could resolve important questions in the Caspian Sea.
The Caspian pipeline could be particularly beneficial for the Nabucco pipeline backed by the European Commission, which would carry gas via Turkey, Bulgaria, Romania and Hungary into Austria and western Europe, and is struggling to find enough gas for its planned 31 billion cubic meter capacity.
Nabucco is regarded as a rival to Russia's South Stream project, intended to deliver 63 bcm of Central Asian and Russian natural gas to Europe under the Black Sea.