Russia's gas giant Gazprom has agreed to cut natural gas prices to Bulgaria by just over 11 percent, Economy and Energy Minister Delyan Dobrev said after talks in Moscow on Friday.

"We negotiated to receive a discount on the price of gas, which according to preliminary estimates will amount to a little over 11 percent -- 11.1 percent," Dobrev told BNR national radio from Moscow, following a meeting with Gazprom chief executive Alexei Miller.

"We agreed to get this discount as of April 1 to be valid over the next nine months," he said.

A key issue in the talks was speeding up the South Stream pipeline to bring Russian gas to Europe under the Black Sea, Dobrev added.

Bulgaria is almost totally dependent on Russian gas for its energy needs and currently pays about $600 (450 euros) per 1,000 cubic metres of gas.

The country also transits 12 to 15 billion cubic metres of Russian gas annually to neighbouring Turkey, Greece and Macedonia.

Dobrev arrived for talks in Moscow late Thursday, a day after Bulgaria's government announced its decision to abandon a joint project with Russia for a 2,000-megawatt nuclear power plant in the northern town of Belene.

The plant, to have been built by Russia's Atomstroyexport, was seen as strategic by the company as it was going to be their first in the European Union.

Feasibility questions, price haggling and safety concerns however bogged down the long-delayed project, which was under discussion for over 30 years.

Russia earlier threatened to sue Bulgaria for $1.0 billion if it dropped the deal, but Dobrev was cited by BNR as saying the issue was not raised in Moscow on Friday.

The talks with Miller and Russian Vice Premier Igor Sechin were "very useful" and held "in a friendly manner," Dobrev said.

In a move to dissuade Russia from taking legal action, Bulgaria said it would pay for the first nearly-finished 1,000-megawatt reactor at Belene to be ready by October and would install it on the site of its existing nuclear plant at Kozloduy.

"They said this was a different project that would necessitate changes to the initial plans for a two-reactor plant... (and) that it would take several more years," Dobrev said of his Russian interlocutors' reaction.

But they added it "was possible," he said.

The Bulgarian government had said it would review the possibility of constructing a gas-fired plant at Belene and Gazprom noted Friday it was interested in participating, Dobrev added.

Bulgaria's left-wing opposition on Friday threatened to call a no-confidence vote in parliament over the failed Belene project.