Fischer, who is an adviser to the European Union-backed Nabucco pipeline consortium led by Germany's utility RWE, in an interview with German business daily Handelsblatt this week said the project was a political tool launched by the Kremlin to the detriment of Europe's interests.
The comments drew so much ire that state-owned Russian news agency RIA Novosti organized a video conference with Russian gas experts in Moscow, who commented on the interview to reporters in Berlin.
The experts strongly refuted Fischer's remarks. They're a sign that the consortium behind the Nabucco pipeline "seriously fears the competition from South Stream," Andrei Konoplyanik, an adviser to the board of the Gazprom Bank, said Thursday.
Rather, Nabucco, a project designed to make Europe less dependent on Russian energy imports, is unrealistic because it hasn't secured any gas deliveries yet, Konoplyanik said.
"It's very well possible that Nabucco won't be realized," he added.
South Stream has already secured Central Asian gas and could be supplied with Russian sources as well. "That's the pipeline's main competitive advantage," said Anatoly Dmitrievsky, director of the Institute for Oil and Gas of the Russian Academy of Sciences in Moscow.
Nabucco is designed to transport 1.1 trillion cubic feet of natural gas per year from Caspian and Middle Eastern sources to Europe, bypassing Russia. Consortium officials are optimistic that Nabucco will be feed by gas from Azerbaijan and Iraq.
The consortium is "confident that there are enough resources in Azerbaijan and Iraq for Nabucco to come into operation in 2015," Christian Dolezal, a spokesman for Nabucco, told United Press International in response to e-mail questions.
Moscow launched South Stream as a rival, intended to move 2.2 trillion cubic feet of gas per year from Russia under the Black Sea to Bulgaria and then on to Western Europe.
The Russian aim is also to go around Ukraine, which transports 80 percent of the Russian natural gas bound for Europe but has in the past temporarily halted supplies to Europe due to price rows with Moscow.
Some observers have indicated that both gas consortiums could merge but Dmitrievsky said such a plan could only materialize "if Europe drops its diversification strategy."
(Additional reporting by Daniel Graeber.)