Greek Development Minister Christos Folias said the development of South Stream was on schedule, with the project expected to go online in 2014. Greek lawmakers signed the agreement in April, calling it a "historic" development.

South Stream eventually may replace a portion of the Blue Stream pipeline from Russia to Turkey. It will travel 560 miles through the Black Sea from Russia to the Bulgarian port of Varna.

Russia hopes South Stream will rival the Western-backed Nabucco pipeline, though South Stream is plagued by financial and environmental concerns.

Folias, however, said South Stream was not a rival to Nabucco, saying the additional line would satisfy rising regional energy demands, B92 reported.

The $10 billion pipeline is expected to transport around 1.1 trillion cubic feet of natural gas per year.