Russian Prime Minister Vladimir Putin said on Thursday gas supplies to Ukraine would be suspended if it does not pay for Russia's gas by Saturday.
"If this payment is not made as a result of the recent operations and arrests of some officials, it will lead to the haltof our energy supplies both to consumers in Ukraine and to consumers in Europe," Putin was quoted as saying by the Interfax news agency.
His remarks came a day after Ukraine's national security service broke into the headquarters of the state gas monopoly Naftogaz in an investigation into alleged gas diversion.
"Actions taken by the Ukrainian law enforcers and officials against Naftogaz and the declared intention to seize gas on the Ukrainian territory are a source of our extreme concern," Putin told a meeting of the governmental presidium.
Putin said the Russian energy giant Gazprom's attempts to get official information on the issue have not yielded any results.
"We are following the events taking place in Ukraine solely as its internal affair. At the same time, we cannot but point out the possible negative consequences of the events for energy deliveries to consumers in Ukraine and consumers in Europe," he said.
In a separate report, Interfax quoted Oleksandr Shlapak, deputy head of the Ukrainian presidential secretariat, as saying that Ukraine may fully pay Gazprom for the Russian gas supplied in February as early as Thursday.
Russia cut off gas supplies to Ukraine on Jan. 1 over a pricing dispute, and halted gas deliveries via Ukraine to Europe a week later, leaving millions of Europeans shivering in the depths of winter.
Gazprom resumed gas shipments to Europe through Ukraine on Jan.20 after Russia and Ukraine signed gas supply deals that ended the dispute between the two countries.
Russia supplies a quarter of EU's gas needs, with 80 percent of it sent through Ukrainian pipelines.