Matthew Bryza, a top U.S. envoy to Europe, said at an international energy summit in Turkey that U.S. President Barack Obama did not favor any Iranian involvement in Nabucco, the Azeri Press Agency reports.
The "Obama administration does not take positive approach toward participation of Iran in the project at present," he said.
Obama renewed comprehensive sanctions on Iran, in part banning U.S. companies from doing business in the Iranian energy sector. The United States and its Western allies back the $10.7 billion Nabucco gas pipeline as a way to ease the regional dependency on Russian natural gas.
Nabucco would bring natural gas from ports in the Caspian Sea to European markets.
The Iranian ambassador to Georgia, Mojtaba Damirchi, said in February that European parties had approached Iran about participating in the project.
Europe sees Nabucco as a near panacea for its energy woes, though observers worry over gas supplies for the project. Iran, for its part, holds some of the largest natural gas reserves in the world, second only to Russia.