Russian gas supplies to Europe via Ukraine are due to end on Wednesday, when a five-year deal between Ukrainian gas transit operator Naftogaz and Russia's Gazprom expires.
Ukrainian President Volodymyr Zelensky said his country would not allow Russia to “earn additional billions from our blood” and gave the EU a year to prepare.
The EU has significantly cut gas imports from Russia since it began its full-scale invasion of Ukraine in 2022, but a number of eastern member states are still heavily dependent on supplies, making Russia about 5 billion bpd. euros ($5.2bn; £4.2bn) a year.
The European Commission said the continent's gas system is “resilient and flexible” and that it has sufficient capacity to handle the end of transit through Ukraine.
Russian gas accounts for less than 10% of EU gas imports in 2023. according to data from the blockcompared to 40% in 2021.
But several EU members, including Slovakia and Austria, continue to import significant quantities of gas from Russia.
Austria's energy regulator said it does not foresee a supply disruption as it has diversified sources and accumulated reserves.
But Ukraine's decision has already caused serious tension with Slovakia, which is now the main entry point for Russian gas into the EU and has earned transit fees from moving the gas to Austria, Hungary and Italy.
On Friday, the Prime Minister of Slovakia, Robert Fico, who had just done a surprise visit to Moscow for talks with Russian President Vladimir Putin – threatened to stop the supply of electricity to Ukraine.
This prompted Zelensky to accuse him of helping Putin “finance the war and weaken Ukraine.”
“Fico is involving Slovakia in Russia's attempts to cause more suffering to Ukrainians,” the Ukrainian president said.
Poland has offered to support Kiev if Slovakia cuts off electricity exports – supplies that are crucial to Ukraine, whose power plants are under regular attack from Russia.
Moldova, which is not part of the EU, could be seriously affected by the end of the transit agreement. The gas powers a power plant that Moldova relies on for most of its electricity needs. It also supplied the Russian-backed breakaway region of Transnistria, a small sliver of land sandwiched between Moldova and Ukraine.
Moldova's Energy Minister Constantin Borosan said the government had taken steps to ensure stable electricity supplies in the country, but urged citizens to conserve energy. A 60-day state of emergency in the energy sector has been in force in Moldova since mid-December.
President Maya Sandhu has accused the Kremlin of “blackmail” that is likely aimed at destabilizing her country ahead of general elections in 2025. The Moldovan government also said it had offered aid to Transnistria.
Russia has been transporting gas to Europe through Ukraine since 1991.
As the EU has reduced its dependence on Russian gas, it has found alternative sources in liquefied natural gas (LNG) from Qatar and the US, as well as gas from Norway.
After the Ukrainian transit route is cut, the Black Sea “Turkish Stream” – which reaches Turkey, Hungary and Serbia – will be the only supply of Russian gas to European countries.
In December, the European Commission lay out plans it said it would enable EU member states to completely replace gas transit through Ukraine.
Under the EU's contingency plans, affected countries will be supplied with Greek, Turkish and Romanian gas from the Trans-Balkan route, while Norwegian gas will be piped through Poland. More supplies will also reach Central Europe via Germany.