Ukraine says it has enough reserves to last for months
Russian gas giant Gazprom has accused Ukraine of stealing gas meant for other European countries.
"The Ukrainian side openly admits it is stealing gas and has no shame about it," company spokesman Sergei Kupriyanov said.
The accusation came after Russia ceased shipments of gas to Ukraine on Thursday amid a row over payments and prices.
Ukraine's state gas company denied illegally siphoning Russian gas, saying it was ensuring the export supply.
Ukraine has insisted it will not interfere with gas transported from Russia to other states via its pipelines, as it has enough gas in its reserves to look after its own needs for some time.
EU countries have not reported any reduction in gas deliveries via Ukraine.
Valentin Zemlyansky, a spokesman for Ukraine's state gas company Naftogaz, told AFP news agency in Kiev that his country was "not stealing gas".
"We are removing gas for technical purposes, in order to ensure the transit of Russian exports," he said.
Naftogaz said earlier it was diverting some gas to maintain pressure in the pipeline network.
Ferran Tarradellas, spokesman for EU Energy Commissioner Andris Piebalgs, told AFP that volumes of gas received were still normal as of Friday morning.
Pipes across Ukraine carry about a fifth of the EU's gas needs. A similar row between Gazprom and Ukraine at the beginning of 2006 led to gas shortages in several EU countries.
The EU has urged Russia and Ukraine to resume negotiations and not to let the dispute disrupt supplies to Europe.
But a spokesman for the Czech Republic, the current holder of the EU presidency, said at the moment it was "a bilateral problem".
"We are not going to interfere until the moment when the pressure of gas will reach low limits," he added.
The Gazprom spokesman also said Ukraine was limiting the amount of gas to be shipped to Europe on Saturday, to only 296m cubic metres instead of the 303m the Russian company had requested.
Talks between the two sides over the supply of gas to Ukraine broke down this week, as the 2008 deal expired.
There are several contentious issues
- Ukraine says it has paid $1.5bn (£1bn) in outstanding gas bills to Gazprom, via a Swiss company - but not late-payment fines. A Gazprom spokesman said the money should clear by 11 January, but that $614m would still be outstanding
- Gazprom wants to increase the price Ukraine pays for gas, from the $179.50 per 1,000 cubic metres Kiev paid in 2008. Gazprom asked for $250. Naftogaz said no, then offered $235. Gazprom has withdrawn its first offer and now wants $418 - nearer the market rate
- Ukraine wants to increase the amount it charges Gazprom for carrying Russian gas west. Without an agreement, the two sides are negotiating prices and amounts day by day
Ukrainian President Viktor Yushchenko said on Thursday he was hopeful that negotiations on a new contract could be completed by 7 January, and that the sides were "close to a compromise".
But it is not clear when talks between the two parties will resume.
A Ukrainian delegation has been visiting Prague and Brussels, seeking support, while Russian Deputy Foreign Minister Alexander Grushko called for an emergency session of the European Parliament, where Russia could present its case.