MOSCOW: Russia and Ukraine traded blame on Tuesday as a dispute between the two bitter ex-Soviet rivals triggered major gas cuts in Europe in a dramatic escalation the EU slammed as unacceptable.

Russian gas giant Gazprom's number-two executive said Ukraine had shut down three of four strategic pipelines that carry Russian gas to customers in Europe, via Ukrainian territory, Russian news agencies reported.

Ukraine's state gas firm Naftogaz charged earlier that Gazprom had sharply reduced volumes of gas it was pumping through Ukraine's pipeline network for European clients, blaming the European shortfalls on the Russian company.

An envoy from the Czech Republic, whose country holds the EU presidency, said after meeting officials in Kiev that "the situation changed very dramatically" overnight and was "getting worse."

In Brussels, the European Union voiced anger over the situation.

"This situation is completely unacceptable," the EU said in a statement, adding that the latest developments were "in clear contradiction with the reassurances given by the highest Russian and Ukrainian authorities."

Russia is the world's largest natural gas producer and provides around one-quarter of the gas used in the European Union, or about 40 percent of the gas the bloc imports.

Top leaders in both Russia and Ukraine had pledged in recent weeks that supplies of Russian gas to Europe shipped via Ukraine would not be disrupted regardless of the direction their bilateral dispute took.

Both countries now however accuse the other of failing to keep their word, and each has scrambled frenetically in recent days to paint the other as an unreliable energy partner for the European Union.

The Gazprom executive, Alexander Medvedev, accused Ukraine of "unprecedented irresponsibility" in the dispute and claimed that the Russian company was powerless to repair the situation itself.

"We are hostages of the situation, we cannot do anything in this situation," he was quoted by Russian news agencies as saying during a visit to London, part of a European tour to drum up support for the Russian position.

In Kiev, a Naftogaz spokesman, Valentin Zemlyansky, warned that European clients should expect immediate "problems" as a result of what he said was Russia's cut in supply.

"We do not understand how we will deliver gas to Europe," Zemlyansky said.

One after another, in the hours after Naftogaz issued its warning, European countries reported sudden and sharp shortfalls in supply of gas from Russia, with Germany the latest EU state to announce a drop.

The shortfalls came a day after Russia's powerful Prime Minister Vladimir Putin ordered Gazprom to cut volumes shipped through Ukraine immediately by amounts corresponding to those Russia claims Ukraine has "stolen."

"Start reducing it from today," Putin told Gazprom chief Alexei Miller in a meeting at the Russian prime minister's country residence.

Experts said the immediate impact on consumers in Europe would be mitigated by the fact that they had consciously stocked up on reserves after a similar Russia-Ukraine dispute caused shortfalls in 2006.

"We are still a long way from end-user customers having a problem," said Chris Weafer, chief strategist for Moscow-based investment bank UralSib.

Estimates however vary on the size of gas stored in reserve by various European countries and on how long those supplies, whose use depends highly on the weather and other seasonal variables, could last.

Gas experts said a picture of how much gas Russia was pumping into Ukraine and how much gas Ukraine was forwarding further downstream could be objectively established by readings of gas metres at key transit points.

The Russia-Ukraine dispute however has become intensely political and neither side appears prepared at present to give much ground in permitting a comprehensive, independent assessment of the situation, they warned.

"At this point the whole level of trust has broken down on both sides," Weafer said. - AFP/de