A top Ukrainian official has warned that European customers could see serious natural gas disruptions in about two weeks if the energy dispute between Russia and Ukraine is not resolved.

Bohdan Sokolovsky is an economic aide to the Ukrainian President.

"If the Ukraine gas system does not get enough gas it will collapse. These problems have not appeared from the Ukrainian side."

The warning came as the Russian gas monopoly Gazprom accused Ukraine of boycotting contract negotiations.

As Russia and Ukraine traded accusations in their bitter dispute over energy prices, four European nations - Romania, Hungary, Poland and Bulgaria - all reported some supply drops in natural gas on Saturday.

Gazprom cut off gas shipments to Ukraine on Thursday.

Then the two sides embarked on offensives, both trying to assure western European nations that they were reliable energy partners and their rival is responsible for any gas shortages.

The Russian delegation says Ukraine is siphoning off natural gas from Russian shipments.

Sergei Yemelyanov is Head of Gazprom Export.

"We have already started taking Russian gas from storages in Europe and today we gave an instruction to increase the amount, and as of today, the overall amount taken from all our storages in Europe is 18.3 million cubic metres."

Russia also accuses Ukraine of refusing to pay 600 million US dollars in fines or negotiate a new price contract for 2009.

The two nations also are at odds over the price Ukraine will pay for natural gas in 2009.

Gazprom has proposed a price jump from 179.50 US dollars to 418 US dollars per thousand cubic meters.

Russia supplies Ukraine with natural gas and also sends 80 percent of its gas supplies to Europe through pipelines in Ukraine.

The stakes in the dispute are high because Europe relies on Russia for a quarter of its gas needs.

The European Union has urged Moscow and Kiev to find an "urgent solution" to the dispute and announced it will host a meeting on Friday with experts from the two countries to discuss natural gas shipments to the 27-nation bloc.