Europe sees the Nabucco gas pipeline as a way to ease the Russian grip on the regional energy sector. The project has significant political support, but little in terms of firm commitments from potential gas suppliers.
Richard Morningstar, the U.S. envoy to Eurasia for energy, told officials in Turkey last week that Iran was "not in a position" to bring its gas to European customers through Nabucco.
Iranian Foreign Minister Manouchehr Mottaki told the Fars News Agency in response that U.S. officials are not the authority on Nabucco gas supplies.
"We have never heard that Europeans have entrusted the Americans with their authority to decide on the pipeline," he said.
Nabucco would bring as much as 1.1 trillion cubic feet of natural gas from suppliers in the Caspian region and the Middle East to European consumers each year. The pipeline would run from the Caspian region through Turkey to Austria along a route through Bulgaria, Romania and Hungary.
Tehran, meanwhile, points out that it holds 16 percent of the world's gas reserves, second only to Russia.
"Speaking about the Nabucco pipeline without Iran's participation would amount to nothing but a pipeline void of gas," said Mottaki.