Russia and Bulgaria pressed the EU on Monday to approve the controversial South Stream gas pipeline, a project that would bypass Ukraine and which Brussels views critically.
Having suspended preparations for the project last month at the height of the crisis between Moscow and Kiev, EU member Bulgaria changed tack to row back in behind the Russians.
Russian Foreign Minister Sergey Lavrov told a press conference in the Bulgarian capital that "we hope the European Commission will adopt a reasonable approach ... without political considerations."
Meanwhile Bulgarian Prime Minister Plamen Orecharski voiced optimism that Brussels would accept "the very good arguments" in favour of going ahead with South Stream's Bulgarian section.
Bulgaria froze its involvement in the project on June 8 under pressure from the EU and US, against a backdrop of the crisis in Ukraine, the historic transit path of Russian gas to Europe.
The EU argued that competition regulations covering public tenders had not been respected, especially regarding access of third party countries, and sent Sofia a warning letter over the issue.
The 16-billion-euro ($21.8 billion) South Stream pipeline is an attempt to reduce Moscow's reliance on Ukraine as a transit country for its natural gas following disputes with Kiev in 2006 and 2009 that led to interruptions of gas supplies to Europe.
The EU has called on all 28 member states to resist pressure from the Kremlin over the project. But the union appears deeply divided, with several member states that depend on Russian gas supporting it.
With a capacity of 63 billion cubic metres per year, the main pipeline would stretch nearly 2,500 kilometres (1,500 miles) from Russia under the Black Sea to Bulgaria, Serbia, Hungary and Slovenia before reaching a terminal in Italy.