Russia and Turkey have signed an agreement to build a gas pipeline from Russia, a project that was suspended amid tensions between the two countries.
The TurkStream pipeline would bring Russian natural gas to Europe on a southern route that would bypass Ukraine.
"The agreement provides for the construction of two lines of the main pipeline across the bottom of the Black Sea," said Aleksei Miller, head of the state-owned Russian energy giant Gazprom.
Miller said the lines would be built by the end of 2019, with the pipeline planned to carry Russian gas to Turkey and possibly European Union member Greece.
The agreement on October 10 came on the sidelines of the World Energy Congress in Istanbul, where Russian President Vladimir Putin met his Turkish counterpart, Recep Tayyip Erdogan, for talks.
It was the Russian leader's first visit to Turkey since November when he attended the Group of 20 summit in Antalya.
"I am convinced that the process of normalization of our ties will continue rapidly," Erdogan told reporters during a joint news conference.
Russia froze talks on TurkStream when Turkish-Russian relations plummeted after the downing of a Russian fighter jet on the Syrian border by Turkish forces in November, with Moscow imposing trade and travel sanctions against Turkey and Russian and Turkish officials making personal attacks against each other.
But a letter of regret from Erdogan on the death of the plane's pilot has led to a normalization of ties.
Russia is also building Turkey's first nuclear power plant, and Erdogan said the sides agreed to accelerate the project.
Putin also said the two leaders agreed on the need to deliver aid to the besieged Syrian city of Aleppo, where Russian air strikes are supporting government forces, although the two sides were at odds over the "security" of the delivery routes.
The Russian leader also said his country was ready to reduce oil production and supports OPEC's initiative to cut production as a way to increase oil prices.
"We believe that a freeze or even a reduction in the production of oil is probably the only appropriate decision for maintaining [the] sustainability of global energy," Putin said.
Putin was due to hold talks with Venezuelan President Nicolas Maduro in Istanbul.
