BRUSSELS — Hungary on Monday said it had asked the European Union to take action against Ukraine for imposing a partial ban on Russian oil exports, arguing the move was jeopardizing Budapest’s energy security.

Kyiv last month adopted sanctions blocking the transit to Central Europe of pipeline crude sold by Moscow’s largest private oil firm, Lukoil, sparking fears of supply shortages in Budapest. Hungary relies on Moscow for 70 percent of its oil imports — and on Lukoil for half that amount.

“Ukraine's decision fundamentally threatens the security of supply in Hungary,” the country’s Foreign Minister Péter Szijjártó said Monday at a meeting of EU envoys in Brussels. “This is an unacceptable step on the part of Ukraine, a country that wants to be a member of the European Union, and with a single decision puts the oil supply …. in fundamental danger.”

Szijjártó claimed that Kyiv's move “clearly violates” the EU's 2014 association agreement with Ukraine. Hungary and Slovakia — also affected by the ban — have now begun talks with the European Commission, he added, a precursor to legal action.

Ukraine argues it is simply trying to throttle a key source of revenue for Russia’s war chest more than two years after its invasion, with estimates showing Moscow made $180 billion from its oil exports last year. The country's energy ministry declined to comment.

The escalating diplomatic spat comes as ties between Ukraine and Hungary hit rock-bottom, with Kyiv last week lashing out at Hungarian PM Viktor Orbán for meeting Russian President Vladimir Putin within a self-styled “peace mission.”

Ukraine's move has also prompted a backlash in Slovakia, which relies heavily on Moscow for oil as well. Although Budapest’s top refiner has already sourced alternative supplies, the sanctions drew a fierce reaction from Slovak PM Robert Fico.

“Slovakia doesn't intend to be a hostage to Ukrainian-Russian relations,” he said on Saturday, following a call with Ukrainian Prime Minister Denys Shmyhal. The ban means the country's central Slovnaft refinery would “receive 40 percent less oil than it needs,” Fico said, arguing it would also reduce Slovak fuel exports to Ukraine that make up a 10th of Kyiv's consumption.

Following Moscow’s invasion of Ukraine, the EU banned imports of Russian oil arriving at the bloc by sea, but allowed landlocked countries like Hungary, Slovakia and the Czech Republic to continue buying supplies via the Russia-to-Europe Druzhba pipeline until they could find an alternative solution.

But Budapest, which has angered Ukraine by holding up EU sanctions against Russia and has stalled Kyiv’s attempts to join the bloc, hasn't tried to find other options, said Isaac Levy, an analyst at the Centre for Research on Energy and Clean Air think tank.

“The reason that the EU gave Hungary an exemption was to allow them time to reduce their reliance on Russian oil through this pipeline,” he said. “But looking at the data since 2021, Hungary has increased its imports of Russian oil via this pipeline by over 50 percent.”

“They should have foreseen the fact the EU was intending to end their exemption allowing them to keep buying Russian oil,” Levy added, “and this should have been something that they planned for … because as we've seen, this is a real risk for their energy security.”

Hungary's foreign ministry and the European Commission didn't respond to requests for comment from POLITICO. Slovakia's economy ministry declined to comment.