A natural gas crisis loomed over Europe as a contract dispute between Russia and Ukraine shut off Russian gas supplies to six countries and reduced gas deliveries to several others.

At least two Bulgarian cities were totally without gas, and nations like Turkey were turning to Iran to bolster their supplies.

In a sharp turnaround, the European Union blasted Russia and Ukraine, saying the sudden cutoff to some of its member countries was "completely unacceptable."

Just a day ago, the EU was trying to downplay any problems from the gas dispute.

New talks on contract

In response, Russia and Ukraine agreed to hold new talks on the contract dispute over Russian natural gas that travels to Europe through Ukraine's pipelines. The two neighbours are locked in a dispute over pricing and overdue payments. Russia cut off supplies to Ukraine on January 1 but had promised to keep gas moving to Europe.

The head of the Ukrainian gas company Naftogaz, Oleh Dubina, said he would travel to Moscow on Thursday for new talks.

He made the decision after speaking to Alexei Miller, chief executive of Gazprom, Russia's state-controlled monopoly gas supplier.

"Given the crisis situation, we are ready to start talks at any moment," said Gazprom spokes-man Sergei Kupriyanov.

Today is Orthodox Christmas, a holiday in both Russia and Ukraine.

Energy dispute

The energy dispute sharply escalated yesterday when six countries on the other end of the pipeline network running from Russia through Ukraine reported a complete shutoff.

Russia supplies Europe with about a quarter of its gas, 80 per cent of which is shipped through Ukraine.

Bulgaria, Greece, Macedonia, Romania, Croatia and Turkey all reported a halt in gas shipments.

Croatia said it was temporarily reducing supplies to industrial customers and urged consumers to use gas sparingly in their homes.

Bulgaria said it had enough gas only "for a few days."

Bulgaria's President Georgi Parvanov said the country could start immediate preparations to relaunch Unit 3 of its Kozlodui nuclear power plant.

Reactors shut down

The ageing two 440-megawatt reactors were shut down two years ago, and Parvanov said one of them could be opened within a month.

Two cities in eastern Bulgaria, Varna and Dobrich, were left with no natural gas supplies.

In Varna, on the Black Sea coast, the shortage left 12,000 households without central heating, amid freezing temperatures.

Turkey's Energy Minister Hilmi Guler confirmed the gas cutoff and said the country was trying to compensate with supplies from other sources, including another Russian pipeline beneath the Black Sea.

During a similar dispute between Ukraine and Russia in 2006, which lasted just three days, several West European countries saw their gas supplies drop by 30 per cent or more.