Executives at the Vienna-based Nabucco pipeline consortium said natural gas from Iraq, Azerbaijan and Turkmenistan could feed the planned $11 billion pipeline.
Europe aims to break the Russian grip on the regional gas sector by moving non-Russian gas through Turkey.
Russian Deputy Prime Minister Igor Sechin said the Nord Stream and South Stream projects meant to diversify Russia's gas transport options would both be working by the time Nabucco comes on stream in 2015.
South Stream, he added, would "take precedence" on gas reserves, Russia's state-run news agency RIA Novosti reports.
His comments come as a Russian delegation wrapped up energy talks last week in gas-rich Turkmenistan.
"Given the estimates of the Turkmen side, as well as European and international experts, the current market situation on the gas track allows us to say -- and I say so without sarcasm -- that there are no prospects for Nabucco," Sechin said.