Russian Prime Minister Vladimir Putin warned his Swedish counterpart Fredrik Reinfeldt, rotating president of the European Union (EU), on Sunday that Ukraine might again have difficulty paying for Russian natural gas.

During a telephone conversation, Putin urged EU attention to possible problems in Ukraine's payment for Russian gas, news agencies quoted the Russian government's press office as saying.

"Thus, problems may arise in transit of Russian gas to Europe via Ukraine," said the press office.

Putin was reassured by Reinfeldt, whose country currently holds the rotating EU presidency, that he would notify the European Commission of Russia's concerns.

On Friday Putin had already held a telephone conversation with his Ukrainian counterpart Yulia Tymoshenko over the issue, saying that "it seems we are again seeing problems with the payment of our energy supplies (from Ukraine)."

Russia supplies a quarter of EU's gas needs, with 80 percent of it pumped through Ukrainian pipelines. The energy supplier cut off gas shipments to Ukraine for nearly two weeks in January over disputes on pricing and transition fees.