Bulgaria successfully completed a third market test to expand the country's gas transit network from Turkey to Serbia for the TurkStream natural gas pipeline, Bulgartransgaz said on Friday.

State-owned gas transmission system operator Bulgartransgaz announced that after successful testing of the third phase of the project that is estimated to cost 2.77 billion lev ($1.6 billion), it took a final investment decision for the realization of the project for development and expansion of the country's gas transmission system.

The third phase involves economic tests of the possible pipeline between Turkey, Bulgaria and Serbia.

At the end of December 2018, Bulgartransgaz launched a tender for the construction of a new 484-kilometer-long gas pipeline from compressor station Nova Provadia, which will be located around 50 kilometers from the Black Sea coastal city of Varna, to the border with Serbia.

Accordingly, the company said it would enter into binding capacity contracts with the candidates who submitted binding offers.

"The binding nominations submitted by users total 100 percent of the capacity announced within phase three on the Bulgarian-Turkish border and 100 percent of the capacity announced on the Bulgarian-Serbian border," it said.

The deadline for offers was announced as Feb. 15, 2019.

The TurkStream natural gas pipeline has a total capacity of 31.5 billion cubic meters out of which the first line will carry a capacity of 15.75 billion cubic meters of Russian gas to Turkish consumers. The second line will carry another 15.75 billion cubic meters of gas to Europe via Turkey.

The second line of the project to transfer Russian gas to Europe is expected to route through Bulgaria following transmission via Turkey. TurkStream gas plans to run from Turkey to Bulgaria, then Serbia, Hungary and Slovakia.

During his visit to Belgrade last month, Russian President Vladimir Putin said Russia was ready to invest $1.4 billion to extend the TurkStream gas pipeline through Serbia to the rest of Europe.

The Russian president also said the TurkStream gas pipeline is set to become fully operational by the end of 2019.

On the occasion of completing the sea part of the project, a ceremony in Istanbul was held in mid-November with the participation of President Recep Tayyip Erdoğan and Russian President Vladimir Putin.