Putin joined Erdogan in Istanbul on January 8 for the official opening of the TurkStream pipeline -- a project that is part of Moscow's efforts to reduce shipments via Ukraine. The construction began in May 2017 and cost nearly $8 billion.
The pipeline was a sign of "interaction and cooperation for the benefit of our people and the people of all Europe, the whole world," Putin said at the inauguration ceremony.
Spanning more than 930 kilometers under the Black Sea, it will carry 31.5 billion cubic meters (bcm) of Russian gas annually to Turkey's western province, with half of the volume flowing further to the Balkans and Central Europe, including Bulgaria, Serbia, and Hungary.
The ceremony in Istanbul was also attended by the leaders of Serbia and Bulgaria.
Russia has already started European gas deliveries through the pipeline, Bulgarian gas operator Bulgartransgaz said on January 5. The pipeline terminal is near the Turkish village of Kiyikoy, some 20 kilometers from the Bulgarian border.
It’s part of Russia's long-term goal of reducing or ending gas transit through Ukraine with alternate pipeline projects, such as Nord Stream 1 and 2.
Both connect to Germany underwater but the near-completion of Nord Stream 2 has been delayed due to U.S. sanctions.
Russia, which exported nearly 200 bcm to Europe last year, has been supplying gas to the Balkans and Turkey overland though Ukraine, Moldova, and Romania.
Putin and Erdogan are also expected to discuss Syria and Libya, where the two countries support opposing sides, while addressing regional tensions in Iraq and Iran, which have escalated after the U.S. killing of a top Iranian commander.
Putin came to Turkey straight from Syria, where he met with Syrian President Bashar al-Assad.
"The leaders heard military reports on development in various regions of the country," Kremlin spokesman Dmitry Peskov said.