Iran has said it shares Moscow's concern over an offer by the European Union to broker talks on a proposed pipeline to carry natural gas to the West.
The 27-nation bloc agreed on Monday to negotiate a deal between energy-rich former Soviet nations Azerbaijan and Turkmenistan aimed at building a Caspian Sea pipeline that would carry Turkmen gas directly to Europe.
The scheme would boost the EU-backed Nabucco pipeline project. Nabucco, slated to carry natural gas from the Caspian region to Austria via Turkey, is part of an effort to reduce the EU's almost total dependence on Russian imported natural gas.
Russia has said it "regretted" the EU move, saying only the five states bordering the Caspian Sea had the right to settle issues concerning its body of water.
"Outside attempts to meddle in the affairs of the Caspian [Sea]... could very seriously complicate the situation in this region and hamper the ongoing five-party negotiations on the Caspian Sea's legal status," the Russian Foreign Ministry said on Monday.
A statement from Iran's embassy in Moscow said Tehran shared Moscow's concern.
"The two countries oppose this decision, which runs against ecological interests and the authority of each of the five states in solving issues concerning the Caspian Sea," the statement said.