Another project which Mr Putin is determined should go ahead is Russia's South Stream gas pipeline, across the Black Sea and into the heart of the European Union.

BBC: Struggle for Central Asian energy riches

Moscow also tried to hire former Italian Premier Romano Prodi as chairman of a second gas pipeline, South Stream.

CENTERFORSECURITYPOLICY: A Bear energy market

Bulgaria is also involved in two rival gas pipeline projects: Russia's South Stream pipeline and the EU-backed Nabucco pipeline.

BBC: Bulgaria profile