Russia on Tuesday shrugged off a key EU gas pipeline deal with Turkey, branding it economically unsound and driven by overblown fears of dependence on Russian gas, Interfax news agency reported.

"Russia reacts calmly to the signing on July 13... for the gas pipeline project Nabucco with Turkey's participation," an unnamed source in the foreign ministry was quoted as saying.

"We are of the opinion that any gas pipeline network should be based not on geopolitical considerations, but on economic realities... which is not the case for Nabucco," the diplomat said.

Monday's accord signed between Austria, Bulgaria, Hungary, Romania and Turkey is a milestone in the much-delayed, European Union-backed project aimed at cutting Russia's gas monopoly in Europe.

About a quarter of the gas consumed in Europe is sourced from Russia.

"The realisation of this project is unreasonably politicised and often used without basis to exaggerate the issue of overcoming European countries' excessive energy dependence on Russia," the diplomat added.

He added that Russia's own South Stream project to pipe gas to Western Europe was by comparison "much closer to realisation" and "economically grounded".

Russian newspapers earlier Tuesday gloomily described the Nabucco deal as a severe setback for South Stream.

"A gas alliance against Moscow has been concluded," the mass-circulation Komsomolskaya Pravda said, terming the deal "a blow" to Russia.

The official Rossiiskaya Gazeta said: "Experts have for long considered Nabucco as a stillborn project... but now the situation has changed."

"The EU team is now leading in the game between Nabucco and South Stream," the financial daily Vedomosti said in an editorial.

The Kommersant said: "It is evident that Nabucco will lead ahead of South Stream considerably as it has the backing of almost all of Europe... South Stream cannot boast of such backing."

The 3,300-kilometre (2,000-mile) Nabucco conduit aims to become operational in 2014 at an estimated cost of 7.9 billion euros (10.9 billion dollars), but there is still lingering uncertainty over who will supply the gas.

It is due to pump billions of cubic metres from the Caspian Sea to Austria via Turkey and the Balkans, bypassing Russia which has been accused of using gas as a weapon by cutting it off in disputes with its neighbours.