A planned Russian-backed oil pipeline linking a Bulgarian Black Sea port with the Aegean faces "problems" with the government in Sofia, Russia's energy minister said on Wednesday.

"I think we will have problems because the Bulgarian side is insisting on us raising the ecological effectiveness of the project," Russian Energy Minister Sergei Shmatko told Russian MPs, quoted by news agencies.

Shmatko added that the Bulgarian leadership viewed the planned system for distributing dividends from the Burgas-Alexandroupolis pipeline as "not very advantageous for Bulgaria."

His comment came as Russian and Bulgarian energy officials prepare to meet in Sofia on December 11.

Bulgaria's pro-Western Prime Minister Boyko Borisov said following his election this summer that Sofia would review several major Russian-backed energy projects.

The oil pipeline, which would stretch 280 kilometres (174 miles) from the Bulgarian port of Burgas to the Greek port of Alexandroupolis, would carry Caspian oil to Western Europe bypassing busy shipping routes.

Russia, Greece and Bulgaria signed an agreement in 2007 on the pipeline project, which is 51-percent controlled by a Russian consortium made up of state-owned oil companies Transneft, Rosneft and Gazprom Neft.

Currently most of the Caspian oil destined for Europe and the United States is transported via the North Sea in tankers that pass through Turkey's Bosphorus and Dardanelles straits.