Russian President Vladimir has required a "rock-solid guarantee" that South Stream, if continued, would be carried through.

At a press conference on the occasion of talks with Turkish counterpart Recep Tayyip Erdogan, Putin has made clear the two countries would go on with Turkish Stream gas pipeline, which was announced as an alternative to South Stream at the end of 2014.

"We never politicize issues of economic cooperation," Putin has told the media, amid efforts to renew energy cooperation with Russia from the Bulgarian side

"We see that the Bulgarian side would like to return to this project... But intentions alone are not enough," the Russian head of state has said.

Due to the moves by the EU Commission to pressure Bulgaria into blocking the construction Russia "suffered certain losses" and now needs "rock-solid legal guarantees... They are not present, though."