Brussels: The United Nations and the EU on Wednesday warned that plans to hold separatist leadership polls in east Ukraine at the weekend would undermine peace efforts, as rebels launched early voting on the internet.
Kiev and Moscow meanwhile went into another round of EU-brokered gas talks in Brussels to end a months-long supply cut that threatens to hit parts of Europe this winter.
Russia stirred tensions with its war-torn neighbour by announcing that it would recognise polls pro-Kremlin insurgents intend to stage on Sunday, drawing sharp criticism.
The vote "will seriously undermine the Minsk Protocol and Memorandum, which need to be urgently implemented in full," UN Secretary General Ban Ki-moon said in a statement, referring to the ceasefire agreement signed by Kiev and the rebels on September 5.
In a round of telephone diplomacy ahead of the controversial rebel polls, Ukrainian President Petro Poroshenko also discussed the issue with EU foreign policy chief Federica Mogherini.
The EU condemned Moscow`s intention to recognise the polls. "We deplore (Foreign) Minister (Sergei) Lavrov`s remarks about Russia`s forthcoming recognition of the elections," it said.
The Russian foreign minister had said Tuesday that the rebel elections in Ukraine`s east should "go ahead as agreed" and that Russia would "recognise the results".
The remarks were followed by an EU decision to keep sanctions in place against Moscow for its role in the crisis.
The pro-Russian separatists of the so-called Donetsk People`s Republic meanwhile launched early internet polling Wednesday for absentee voters.
The gas standoff between Ukraine and Russia was also in focus as the EU tried to broker a deal amid fears that the supply cut could spell problems for large parts of Europe in winter.
Speaking after meeting his Ukrainian counterpart Yuri Prodan in Brussels, EU Energy Commissioner Guenther Oettinger said he would meet with his Russian counterpart Alexander Novak before all three sat down together.
"Our common ambition is to come to an interim solution, to come to a winter package ... to solve our security of supply," Oettinger told reporters.
In an interview with German television ZDF earlier, Oettinger put the talks` chances of success at no more than 50 percent.
Several acrimonious rounds of talks have failed to resolve a dispute stemming from Kiev`s refusal to pay a higher rate imposed by Moscow after the February ouster of Ukraine`s Kremlin-backed president.
Russia`s state energy holding company Gazprom cut Ukraine`s gas deliveries in June -- the third such interruption in less than 10 years.
The cut did not immediately impact European clients which receive about half their Russian shipments via Ukraine, but EU nations fear that Ukraine may tap into gas deliveries out of desperation during the winter.
The two sides have reached a tentative price deal that would see Russia charge about 20 percent less at $385 (302 euros) per 1,000 cubic metres for the coming six months.
But there is still no agreement over Ukraine`s debt repayments or how it will pay for the new deliveries.
Analysts warned that the threat of a gas cut would hang over Europe until a final agreement between Moscow and Kiev is reached.
"A gas deal is critical. Until a deal has been formally agreed the risk of failure and the threat of disruptions to EU customers remain," said Chris Weafer of Moscow`s Macro-Advisory consultancy.
"The issue for Moscow is who will pay both the arrears of $1.45 billion immediately and a further $1.55 billion by the year-end, and the upfront winter gas supply cost of approximately $2.0 billion."
The European Commission said last week that Kiev had requested a further 2.0-billion-euro ($2.5-billion) loan from Brussels to help cover the debt.
In eastern Ukraine, rebel leader Alexander Zakharchenko said he was making battle preparations as well as campaigning ahead of the separatist vote.
"We are preparing for war," he was quoted by Interfax news agency as saying. "De facto there was no truce. Attacks on our cities continued," he said.
Rebel commanders near the town of Telmanove south of Donetsk told AFP journalists they are preparing for a long fight. Some were seen constructing more permanent winter shelter out of wood.
Ukraine staged its own elections on Sunday in which pro-European forces scored a decisive victory at the expense of parties that once backed closer ties with Russia but now tread a more centrist course.
The poll saw Western-backed Poroshenko`s political bloc and a party led by Prime Minister Arseniy Yatsenyuk come close to the 50 percent of the votes needed to form their own government.
Poroshenko is busy negotiating the makeup of a new coalition that is all but certain to keep Yatsenyuk as premier -- an outcome cheered by Western lenders who view him as a market-friendly proponent of economic change.