Ukraine and Russia blame each other for the gas shutdown
Top EU officials plan to join Russia and Ukraine in high-level talks in Moscow to resolve the gas crisis.
The Russian and Ukrainian governments have confirmed that they will hold talks in Moscow on Saturday.
EU Energy Commissioner Andris Piebalgs and Czech Energy Minister Martin Riman will attend, the commission says.
No gas is flowing via Ukraine to Central and Eastern European countries, some of which are rationing gas amid cold weather and diminishing reserves.
German Chancellor Angela Merkel warned that Russia could damage its reputation as a reliable energy supplier if the row continued.
She is due to meet Russian Prime Minister Vladimir Putin in Germany on Friday.
In a late-night phone call on Thursday, Ukrainian Prime Minister Yulia Tymoshenko agreed with Mr Putin that their two governments should meet at the weekend, her side said.
But, after high-level talks in both Moscow and Kiev, Slovak Prime Minister Robert Fico said he could not see how the two sides could be reconciled any time soon.
"I cannot imagine what would have to happen within 24 hours, or 48 hours, for the gas transit to resume," he said.
"It is practically impossible. The conditions laid by one and the other side are so contrasting that this simply cannot work," he told a news conference.
EU governments are becoming exasperated at Russia and Ukraine for failing to resolve their row, despite an apparent agreement to resume transit supplies of gas, reached on Monday, correspondents say.
Russia shut off gas supplies to Ukraine on New Year's Day, amid a contractual dispute over debts and prices.
It continued pumping gas across Ukraine to European customers, but then halted those supplies after accusing Kiev of siphoning some off.
The European Commission has warned Russian and Ukrainian gas companies that they could be sued for failing to meet their obligations.
Legal action is under way in Serbia, Hungary and Bulgaria, says the BBC's Nick Thorpe in Budapest.
Wider gas network
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