The European Union today demanded the immediate restoration of full gas supplies from Russia as the impact of a price dispute between Moscow and Ukraine worsened.

Greece, Bulgaria, Romania, Turkey and Greece reported virtual closures of supplies, despite assurances from Russian Prime Minister Vladimir Putin that gas would still flow to Europe despite turning off the tap to Ukraine.

A strongly-worded joint statement from the European Commission and the Czech government, now holding the EU Presidency, attacked the failure of both sides to stick to promises not to let their bilateral row spill over.

It said: "Without prior warning and in clear contradiction with the reassurances given by the highest Russian and Ukrainian authorities to the European Union, gas supplies to some EU member States have been substantially cut. This situation is completely unacceptable.

"The Czech EU Presidency and the European Commission demand that gas supplies be restored immediately to the EU and that the two parties (Russia and Ukraine) resume negotiations at once with a view to a definitive settlement of their bilateral commercial dispute."

Moscow last night announced a 20% cut in the volume of gas piped to Europe via Ukraine, which is refusing to pay higher prices demanded by Russia's state-controlled monopoly supplier Gazprom.

Mr Putin, who personally ordered the cut, insisted the company would make up the EU shortfall by sending more gas via other routes.

But today, in the midst of a bitter winter spell, a major energy crisis seemed closer, with at least six EU counties, including Hungary, Poland and the Czech Republic itself, enduring significant shortages.

Today the Czech Presidency and the Commission both pledged to "intensify the dialogue" with Moscow and Kiev, to speed chances of a swift agreement, but there were few signs that either side was likely to respond to outside intervention.

The European Commission still insisted there was no energy crisis, claiming that gas reserves in the EU were sufficient to meet needs while Russia and Ukraine resolved their differences.

Moscow has accused Ukraine of siphoning off gas supplies destined for the EU to make up for last week's Gazprom decision to cut off gas to the country because of unpaid bills and a refusal to accept a New Year price hike.

Ukraine denies the charge, but the EU is now caught in the midst of the conflict and reviewing its energy security policies again after facing the same dilemma in a similar Russia-Ukraine dispute three years ago.

The 2006 dispute prompted the EU to step up its gas storage facilities and look for new gas supply options.

But the EU still depends on Russia for about 25% of its total gas supplies, and the bulk of Russia's gas exports come to the EU via Ukraine.

Gas reserves vary hugely between the EU countries - from an estimated 120 days' worth in France to a reported 15 days in the UK.

Largest EU importers of Russian gas are Italy and Germany - but both countries also have significant alternatives sources and face no immediate threat.

The UK only gets a tiny fraction of its gas supplies direct from Russia - but a large share via France, which relies more heavily on Russia.

And EU members such as Bulgaria, Hungary, Lithuania and Latvia - all former Soviet satellites - are most reliant on Russia.

Today EU officials insisted a swift resumption of what they insisted was a purely commercial dispute between the two countries, would mean little impact on the EU economy.

But a more prolonged row between Russia and Ukraine could have long-lasting consequences.