Russian President Vladimir Putin is to meet with his Turkish counterpart Recep Tayyip Erdogan in Istanbul on Monday.
The trip is prompted by the completion of a new section of the gas pipeline Turkish Stream, according to Turkish media, but regional affairs will also be up for discussion.
Once totally finished, the pipe will connect Russia and Turkey via the Black Sea, reaching the Turkish coast 100 kilometres to the west of Istanbul.
Turkey is one of the biggest consumers of Russian gas. Construction for Turkish Stream began in May 2017. The first section is to supply the Turkish market, the second is to provide south- and south-eastern Europe with Russian gas.
The civil war in Syria has pitted the two nations against each other, with Moscow backing Syrian President Bashar al-Assad while Ankara supports the rebel forces. The topic may be broached in talks on Monday.
Both countries agreed on a deal to create a demilitarized buffer zone in the province of Idlib in September, staving off an assault by Syrian government forces. However, not all insurgents have withdrawn from the area.
The region of Idlib is the last major rebel stronghold in Syria. Around 3 million civilians live there, almost half of them displaced persons.