ANKARA, Nov. 18 (Xinhua) -- Turkey and Russia will inaugurate on Monday in Istanbul the sea section of the TurkStream natural gas pipeline, a major project which will carry Russian gas to Turkey and Europe while bypassing Ukraine.

The transit-free project through the Black Sea consists of two lines, each with a length of 930 km and the capacity to deliver 15.7 billion cubic meters of gas per year.

The first line is intended for gas supplies to Turkish consumers, with 15.75 billion cubic meters of natural gas going to Turkey, while the second will supply gas to southern and southeastern Europe, carrying the rest of the total throughput capacity of 31.5 billion cubic meters.

Notably, Russia is reportedly considering extending the pipeline through Bulgaria and Serbia or through Greece and Italy.

The ceremony on Monday in Istanbul, Turkey's largest city and economic hub, is designed to mark "what is another concrete milestone of the strengthening and diversifying Turkish-Russian energy relationship," said the Turkish presidency in a statement.

"Both countries are determined to maintain their close cooperation in energy like in all the other fields in the coming period," the statement added.

Russian state-owned energy giant Gazprom is planning to start the construction of the overland section of the TurkStream's second gas pipeline in 2019.

Asli Esen, Turkish spokeswoman of TurkStream, said the project will be completed by the end of 2019 as planned, state-run Anadolu Agency reported.

According to the information provided by the TurkStream authorities, the project has been designed to operate for at least 50 years.

For Turkey, a NATO member which emerged in the last decade as a key transit point for alternative gas supplies from the Caspian Sea region, advantages and risks co-exist in the TurkStream project, said experts.

Turkey sees itself as a bridge between gas-production and gas-consuming nations, and hopes to become a regional energy hub by virtue of its proximity to the Greater Middle East, which holds more than 70 percent of global conventional oil and gas reserves.

"Turkey will purchase all the gas that it buys from Russia directly from this new pipeline. This could be considered a move reinforcing its energy security in peace time, but also it could be the opposite in times of crisis," Kerim Has, a Moscow-based analyst on Turkish-Russian relations, told Xinhua.

However, the expert also warned of the possible threat Russia, Turkey's largest gas supplier, could pose to its energy security in case ties between the two countries go sour, as in 2015 when Turkey shot down a Russian fighter plane over Syria, an incident which briefly froze their relations.

Despite later success in overcoming differences and more moves to further bilateral cooperation, the Russian jet crisis still left a bad taste in the mouth of observers wary of Turkey's growing and dangerous dependency on Russian gas.

"At this stage, the TurkStream project will consolidate the actual (energy) corridor role of Turkey but also increase its dependency on Russian gas," Has said.

With a serious lack of indigenous gas reserves, Turkey relies heavily on imported gas, which contributes to 29 percent of its primary energy consumption and almost 50 percent of electricity generation.

"We are trying to diversify our energy mix and we have reached satisfactory results, but we have to go on and find new foreign suppliers and use more renewable energy," a Turkish official told Xinhua on condition of anonymity.