SOFIA - Three consortiums have submitted bids in a 1.4 billion euro ($1.58 billion) tender to build a pipeline to carry Russian natural gas across Bulgaria, state-owned network operator Bulgartransgaz said on Thursday.

"Bulgatransgaz will make its utmost efforts to carry out this project in line with Bulgarian and EU laws," Bulgartransgaz CEO Vladimir Malinov told reporters.

The 484-km (303 mile) pipeline is expected to run from Bulgaria's border with Turkey in the southeast to Serbia to the west, carrying gas from Russia's TurkStream twin pipeline to Turkey.

The link is expected to begin operating by the end of 2019.

Russia's gas exports have became increasingly politicised since Moscow's annexation of Crimea from Ukraine in 2014. Moscow is building TurkStream as part of its efforts to bypass Ukraine, a major route for its gas exports to Europe.

Russian Prime Minister Dmitry Medvedev told his Bulgarian counterpart Boyko Borissov on Monday that Russia needs guarantees from the European Commission prior to choosing Bulgaria as a route for its TurkStream gas pipeline project.

The tender was suspended last month following a request for clarification by a Bulgarian company, which has since withdrawn it.

($1 = 0.8836 euros)

(Reporting by Tsvetelia Tsolova and Angel Krasimirov; editing by Edmund Blair and Jason Neely) ((angel.krasimirov@thomsonreuters.com; +359 888 695 510;))