Mr Putin has been trying to form a Russian-EU gas transit consortium

The prime ministers of Russia and Ukraine are to meet in Moscow in an effort to end the dispute disrupting supplies of Russian gas to Europe.

However, there are sharp divisions within Ukraine over whether to link transit supplies to supplies for Ukraine itself at the negotiations.

The EU has urged Russia and Ukraine to prove they are "credible" partners and said it was their "last chance".

A bid to hold a Moscow gas summit on the same day appears to be floundering.

Some central and east European states have been reduced to rationing gas.

Others have been seeking alternatives to the pipelines carrying Russian gas via Ukraine.

Russia ceased supplies of gas to Ukraine on 1 January after talks on the price Kiev should pay in 2009 collapsed.

On 7 January, it stopped deliveries to Europe via Ukraine, saying it was forced to do so because Kiev was stealing the gas.

Ukrainian officials deny the allegation and accuse Russia of provoking the crisis.

Almost 20 countries in Europe have been affected by what is the worst energy crisis the EU has ever faced, the BBC's Richard Galpin reports from Moscow.

Rival positions

Russian Prime Minister Vladimir Putin, fresh from a visit to Germany, one of Moscow's biggest gas clients, is due to meet his Ukrainian counterpart, Yulia Tymoshenko, on Saturday afternoon.

Ukrainians burn a poster of Mr Putin as a Golem figure turning off a gas pipe

Mr Putin said on Friday that a deal to end the gas crisis could be nearer after he discussed the formation of a gas transit consortium.

He said a deal was being brokered between Russia's Gazprom and EU firms to cover part of the cost of pumping gas from Russia to Europe.

It is not clear whether Ukraine would accept such a deal.

Ukrainian President Viktor Yushchenko has said that the issue of renewing Russian gas supplies to Europe was linked to finalising the 2009 supply contract for Ukraine but Mrs Tymoshenko, his political rival, argued the two issues were not connected.

"The issue of natural gas supplies to Ukraine and the issue of transit are interlinked and must be discussed as a single package," Mr Yushchenko's office said on the eve of the Moscow talks.

Speaking the same day, Mrs Tymoshenko said: "The Ukrainian government does not link the issue of concluding an agreement on [Russian] gas supplies to Ukraine with the issue of resuming gas transit to Europe."

Such a link, she added, would be "groundless and unfair".

She also demanded that Ukraine speak with one voice in the negotiations.

"Simply speaking, I need two things: Don't throw a spoke in the wheel and don't stab any backs," she said in Kiev.

'Last chance'

Russian President Dmitry Medvedev has invited EU leaders to an emergency gas summit on Saturday but it appears that only envoys will be sent, including EU Energy Commissioner Andries Pielbags.

"Yushchenko for the chop" - a slogan at a rally in Moscow

Russian Foreign Minister Sergei Lavrov was scathing about the decision not to send EU heads of state.

"We expect anyone interested in resolving the problem as soon as possible to come to the summit being held in Moscow tomorrow," he said on Friday.

He urged the EU to "show its famous solidarity" and put pressure on Ukraine.

The European Commission has warned that the meeting is a last chance for the two countries to prove they are serious about finding a solution to the dispute.

EU states import a quarter of their gas from Russia and 80% of supplies come via Ukraine.

"The European Commission believes that the meetings in coming days offer the last and best chance for Russia and Ukraine to demonstrate they are serious about resolving this dispute," Commission spokesman Johannes Laitenberger said.

"The gas must flow. We will regard this period as a test case for judging whether or not they are credible partners."