Leaders of Russia and Iran spoke out strongly today against outside interference in Caspian Sea affairs.
The warning came during a summit of the five nations bordering the inland sea that focused on ways to divide the region's substantial energy resources.
Russian President Vladimir Putin, whose trip to Tehran is the first by a Kremlin leader since the Second World War, warned that projects of energy pipelines crossing the Caspian could only be implemented if all five nations support them.
Mr Putin did not name any specific country, but his statement underlined Moscow's strong opposition to US-backed efforts to build pipelines to deliver Central Asian and Caspian hydrocarbons to the West bypassing Russia.
"Projects that may inflict serious environmental damage to the region cannot be implemented without prior discussion by all five Caspian nations," he said.
Mr Putin also emphasised the need for all Caspian nations to prohibit the use of their territory by any outside countries for use of military force against any nation in the region - a clear reference to long-standing rumours that the US might be planning to use Azerbaijan, a former Soviet republic, as a staging ground for any possible military action against Iran.
"We are saying that no Caspian nation should offer its territory to third powers for use of force or military aggression against any Caspian state," Mr Putin said.
Iranian President Mahmoud Ahmadinejad also underlined the need to keep outsiders away from the Caspian.
"All Caspian nations agree on the main issue - that all aspects related to this sea must be settled exclusively by littoral nations," he said. "The Caspian Sea is an inland sea and it only belongs to the Caspian states, therefore only they are entitled to have their ships and military forces here."
The legal status of the Caspian - believed to contain the world's third-largest energy reserves - has been in limbo since the 1991 Soviet collapse, leading to tension and conflicting claims to seabed oil deposits.
Iran, which shared the Caspian's resources equally with the Soviet Union, insists that each coastal nation receive an equal portion of the seabed. Russia, Azerbaijan and Kazakhstan want the division based on the length of each nation's shoreline, which would give Iran a smaller share.
Turkmenistan is also vying for the Caspian's resources.
Mr Putin's visit took place despite warnings of amid hopes that a round of personal diplomacy could help offer a solution to an international stand-off on Iran's nuclear programme.
The Russian leader's trip was thrown into doubt when the Kremlin said on Sunday that he had been informed by Russian special services that suicide attackers might try to kill him in Tehran, but he shrugged off the warning.Reuse content