Gazprom accused Ukraine of stealing relatively small volumes of transit gas, but the accusation suggested Moscow was in no mood for compromise in a re-run of a 2006 argument that led to supply shortages across the European Union.
The company said it was responding to Ukraine's actions by increasing exports via alternative routes, including Belarus.
Sergei Kupriyanov, a Gazprom spokesman, said: "The Ukrainian side openly admits it is stealing gas and is not ashamed of this."
Poland said deliveries from Ukraine had dropped six per cent but were being made up by deliveries through Belarus.
The EU, which receives a fifth of its gas via pipelines through Ukraine, said it considered the dispute between Moscow and Kiev to be a bilateral issue.
The Czech presidency of the EU has called an extraordinary meeting of envoys from the 27-nation bloc for Monday to discuss the gas crisis.
Speaking on Friday, Radek Honzak, a presidency spokesman, said: "We feel that the situation has now escalated to a point that substantiates an extraordinary meeting."
Europe, where temperatures fell below freezing overnight, has enough gas stockpiled to manage without Russian supply for several days, analysts said.
The row could raise new doubts about Moscow's reliability as an energy supplier and fuel suspicions in the West, already running high since Russia's war with Georgia last August, that the Kremlin is bullying its pro-Western neighbours.
Though Russia denies politics is behind the dispute and says it is about prices and debts, the two former Soviet neighbours have clashed over a drive by Viktor Yushchenko, the Ukrainian president, to take his country into the Nato alliance.
If talks between Naftogaz and Gazprom do resume, the gulf between their negotiating positions remains wide.
Alexei Miller, the chief executive of Gazprom, said on Thursday that he wanted Ukraine to pay $418 per 1,000 cubic metres (tcm) of gas, compared with the $179.5 Kiev paid in 2008. Ukraine says the most it can afford to pay is $235.
There are also disputes over the amount Russia will pay for the right to ship its gas to Europe via Ukraine, and the $2bn Gazprom says it has still not received from Kiev in gas arrears.
Naftogaz says it has transferred $1.5bn of the outstanding debt to a Switzerland-registered gas trading company acting as an intermediary, but not the remaining $500m in fines imposed by Gazprom.
Gazprom charges about $500/tcm to customers in the EU, though that is likely to fall by up to half this year.
Gas prices track oil and crude has plummeted in value.