Russia's Gazprom expects to send its first gas through the TurkStream natural gas pipeline to Turkey by the end of December, Gazprom Deputy Chairman Vitaly Markelov said late Tuesday.

He confirmed that the subsea section to transport 31.5 billion cubic meters (bcm) per year from Russia to Turkey and Russia's land section have been constructed while Turkey's onshore section is nearly 73 percent complete.

The project's spokesperson Aslı Esen said on Sunday that the construction of TurkStream project's gas receiving terminal in Kıyıköy, the end point of the offshore pipeline in Turkey, passed a 70 percent threshold, a penultimate step that marks the nearing of completion of the whole project.

She said the physical construction of the Kıyıköy receiving terminal, located approximately 100 kilometers west of Istanbul, is going on smoothly and the whole project will be finalized by the end of 2019, in line with the time schedule.

A series of tests has already started for the safety and integrity of whole natural gas pipeline system before pipelines start gas transmission by the end of 2019. The landfall facility in Anapa, a port town on the Russian coast of Black Sea, has been completed successfully and is on standby.

The above water tie-in (AWTI) procedures - a process of welding the parts of pipelines already laid on the seabed, after being lifted on-board a special ship - are also complete, according to Esen.

AWTI has connected the landfall facility in Russia and the receiving terminal in Turkey end to end along with the offshore section, marking another crucial milestone in the project.

The TurkStream project consists of two lines across the Black Sea, the first of which will serve Turkey with a capacity of 15.75 bcm, while the second line is planned to serve Europe. The second line is expected to go from Turkey through Bulgaria, then to Serbia, Hungary and Slovakia. Each pipeline is 930 kilometers in length, laid at depths reaching 2,200 meters.

The project is the biggest-diameter offshore gas pipeline in the world laid at such depths. The world's largest construction vessel, the Allseas-owned Pioneering Spirit, completed the deep sea pipe-laying.