The prime ministers of Slovakia and Bulgaria will meet Russian counterpart Vladimir Putin to press for a resumption in natural gas deliveries halted by a dispute between Moscow and Ukraine.
At least 15 European nations have seen their supplies stopped or reduced since Russia last week stopped sending gas through Ukrainian pipelines to countries further west.
Bulgaria has lost all supplies and has only a day or two of reserves. Slovakia has lost 97 per cent of its supplies. The two countries' premiers plan to attend talks on Wednesday at Putin's estate outside Moscow.
EU efforts to end the crisis faltered on Tuesday when a deal for monitoring gas flows through Ukraine failed to restore supplies. Russia and Ukraine blamed one another.