The international community has condemned Moscow over its plans to recognise separatist polls in Ukraine as NATO warned of “unusual” Russian military manoeuvres in European airspace.

Ukrainian and Russian ministers meanwhile held 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.

Overshadowing the talks, UN chief Ban Ki-moon and the European Union condemned the plans by the rebels to stage elections on Sunday in areas of eastern Ukraine under their control.

The vote “will seriously undermine” peace agreements reached in the Belarus capital of Minsk in September, Ban said, adding that the agreements “need to be urgently implemented in full”.

The EU echoed his concerns that the polls threatened the fragile peace process.

• Russian warplanes intercepted over Europe
• Cold War flashbacks in search for mystery sub

The pro-Russian separatists of the so-called Donetsk People’s Republic launched early internet polling on Wednesday for absentee voters.

Russia has said it would recognise the results of the elections, stirring further tension with Ukraine and its allies, the US and the EU.

Moscow has also rejected Western accusations that it has sent troops and weapons to support the armed uprising in Ukraine’s east, in which around 3700 people have been killed since April.

The EU and US have imposed the harshest sanctions on Moscow since the end of the Cold War over its backing for separatist rebels. The EU kept the sanctions in place following a review earlier this week.

Against a backdrop of heightened tensions with Moscow, NATO on Wednesday said it had tracked and intercepted four groups of Russian warplanes “conducting significant military manoeuvres” in European airspace over the past two days.

“These sizeable Russian flights represent an unusual level of air activity over European airspace,” NATO said.

The planes, which included strategic bombers, fighters and tanker aircraft, were detected over the Baltic Sea, North Sea/Atlantic Ocean and the Black Sea on Tuesday and Wednesday, it said.

Ukraine president Petro Poroshenko. Photo: Getty

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.”

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 President Petro Poroshenko’s political bloc and a party led by Prime Minister Arseniy Yatsenyuk come close to the 50 per cent 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.

The gas stand-off 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.

EU officials said talks involving Ukrainian Energy Minister Yuri Prodan, EU Energy Commissioner Guenther Oettinger and their Russian counterpart Alexander Novak were going late into the evening.

They said a press conference could be held early on Thursday if there was an agreement overnight.

“Our common ambition is to come to an interim solution, to come to a winter package … to solve our security of supply,” Oettinger said.

In an interview with German television ZDF earlier, Oettinger put the talks’ chances of success at no more than 50 per cent.