Ukraine has repeatedly denied Moscow's allegation it was stealing gas
Russian PM Vladimir Putin has said gas supplies to Europe via Ukraine can resume once the European Commission has signed a deal on the transit of gas.
He also said independent observers to verify the gas flow must be in place before Russia resumes the supply.
Moscow has confirmed that Ukraine has already re-signed a deal on the transit of Russian gas "without conditions".
The cut in Russian gas supplies has left many people in Central and Eastern Europe struggling to keep warm.
Experts say it will take up to three days for Russian gas to reach some parts of Europe even if Russia agrees in the next few hours to turn the taps back on.
EU monitors are being deployed to check the pipeline flow when it resumes.
The European Commission said all Russian conditions regarding the transit of its gas to European markets via Ukrainian pipelines had been met and "there are absolutely no reasons not to start gas supplies again".
"Prime Minister Putin confirmed that as soon as the monitors are fully deployed, the gas supply could start again," European Commission spokesman Johannes Laitenberger said.
But Mr Putin also said the Commission must sign off on the deal between Russia and Ukraine before the gas would flow.
The issue will be discussed by European Union ministers at an emergency meeting on Monday, set to begin at 1330 GMT.
The chief executive of Russia's state-owned energy giant Gazprom, Alexei Miller, and Russian Deputy Prime Minister Igor Sechin were on their way to Brussels for talks, Russia's Interfax news agency reported.
Ukrainian Deputy Prime Minister Grygory Nemyrya and the head of Ukrainian state energy company Naftogaz, Oleg Dubina, were also heading to Brussels.
Russia cut supplies to Ukraine on New Year's Day in a dispute over pricing that remains unresolved.
At the weekend it seemed a deal had been done for Gazprom to restart gas supplies to Europe via Ukraine, following frantic EU shuttle diplomacy.
Both Russia and Ukraine had signed an agreement to allow international monitors to observe the flow of natural gas from Russia to Europe via the Ukraine.
But later, Russian President Dmitry Medvedev said Ukraine had added provisos to the accord that were unacceptable to Russia.
Moscow alleged that Ukraine had added a clause denying it owed Russia for past supplies of gas.
The Ukrainian president's envoy for energy security, Bohdan Sokolovsky, accused Russia of delaying tactics, saying "maybe they simply do not have gas, and they know about it, but they are too ashamed to tell the whole world".
The BBC's Gabriel Gatehouse in Kiev says it appears that Ukraine's add-ons relate to the thorny question of Ukraine's gas debts to Russia, and whether or not Kiev had been siphoning off gas destined for European customers.
The dispute has left hundreds of thousands of people without heating during one of the harshest winters in many years.
At their meeting, EU ministers will examine ways of preventing a repeat of the crisis.
The EU gets a quarter of its gas supplies from Russia, 80% of which passes through Ukraine.
The price Ukraine should pay Russia for its gas in the coming year, and how much Russia should pay Ukraine in return for transporting gas to Europe has yet to be agreed.
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