Ukraine has stopped importing Russian gas last Friday following a pricing dispute with Russia’s state export monopoly Gazprom.
The announcement came weeks before Kiev is due to sign a free-trade agreement with the EU – a decision opposed by Russia who sees it as Ukraine escaping from its sphere of influence.
"There have been no supplies to Naftogaz since Friday," an industry source said, referring to the Ukrainian state-owned energy company that buys Russian gas.
A source in Ukraine's gas industry also said that the gas pipeline operator Ukrtransgaz had ordered Naftogaz to stop purchases of Russian gas on Friday.
Around half of the gas Russia supplies to Europe is transported via Ukraine, which makes the whole issue rather sensitive for the rest of the continent.
However an official at Gazprom said transit flows of Russian gas to European clients via Ukraine were continuing unaffected. "All requests for exports are being fulfilled," he said.
Both Gazprom and Naftogaz declined to comment.
The price of gas Ukraine pays to Russia has been at heart of the dispute that puts energy security of the whole Europe at risk. Ukraine pays around $400 per 1,000 cubic metres of Russian gas, one of the highest prices in Europe. Recently, it has asked Moscow to ease the terms, as it considers them to be excessive and unaffordable for its debt-ridden economy.
Last month, Gazprom raised the stakes in the stand-off, saying Ukraine had failed to pay for August deliveries in full.
The dispute has raised concerns of a new "gas war" over prices between the two countries, similar to those in the winters of 2006 and 2009 which caused supplies to be disrupted to Ukraine and the rest of Europe.
Kiev has been trying to reduce its dependence on energy supplies from Russia by fostering closer relation with Europe reducing gas intake from Russia.
The agreements with the EU on association and free trade, expected to be signed at a summit on 28 November, offer the 46 million inhabitants of the former Soviet republic the chance to shift west away from Russia.