The EU's Czech presidency demanded the "immediate resumption" of full gas supplies to EU member states, following drops recorded in Poland and Hungary due to Russia's dispute with Ukraine.
"The European Union calls for an urgent solution to the commercial dispute on gas supplies from the Russian Federation to Ukraine, and for an immediate resumption of full deliveries of gas to the EU member states," the EU presidency said in a statement on Friday.
"Energy relations between the EU and its neighbours should be based on reliability and predictability. Existing commitments to supply and transit have to be honoured under all circumstances," it added.
The European Commission, in a separate statement, said it had received reports from Hungary and Poland of "irregularities in gas received through the Ukrainian gas pipelines."
Hungary has seen a drop of around 10 million cubic meters, almost a quarter of the contracted supply, while Poland has seen a six-percent fall, it said.
In the Polish case the shortfall was being offset by increased volumes coming from Russia via Belarus.
"I will be in contact with all the parties involved to identify the causes of the irregularities and ask for the immediate resumption of full deliveries of gas to the EU members" EU Energy Commissioner Andris Piebalgs stated.
Russia cut supplies for the Ukrainian market on New Year's Day over a payments dispute.
Moscow yesterday accused Ukraine of "stealing" gas bound for European customers, a charge denied by Kiev which levelled its own accusations and the first signs emerged of a drop in supplies to the EU.