Officials from Moscow and Kyiv are due to gather in Berlin on July 17 for EU-backed talks on the future of the transit of Russian gas through Ukraine.
Russian gas giant Gazprom has already dramatically reduced the volume of gas transiting via Ukraine, as Moscow and Kyiv remain at loggerheads over Russia's annexation of Ukraine's Crimea region and its support for separatists in eastern Ukraine.
Kyiv is concerned about the loss of revenue from transit taxes and being left out of routes for new gas pipelines.
The talks will focus on Gazprom's plan to build the Nord Stream 2 gas pipeline and put it into operation by the end of next year. Nord Stream 2 would bring gas to Germany via the Baltic Sea, bypassing Ukraine.
The pipeline will follow the course of the existing Nord Stream 1 and will double the quantity of Russian gas imported by Germany -- the European Union's most powerful economy -- via this route.
The meeting will bring together delegations from Gazprom and its Ukrainian counterpart, Naftogaz, which have been locked in legal battles for years.
Russian Energy Minister Aleksandr Novak and Ukrainian Foreign Minister Pavlo Klimkin will also attend.
The Nord Stream 2 project has been criticized by U.S. President Donald Trump.
Germany has long insisted this is a purely "commercial" project and in March lifted the final obstacles to its construction.
The United States has an interest in selling liquefied natural gas (LNG) to Europe via ships.
Last winter, Gazprom raised exports to the continent to a record high thanks to cold weather.
