Russia's gas monopoly Gazprom said yesterday that neighbouring Ukraine was using more Russian gas than agreed, cutting onward supplies to Europe.
But Ukraine, a key transit route for Russia's huge supplies to Europe, said it was abiding by all its obligations despite soaring domestic gas use due to cold weather.
The comments appear to reignite a row early this month when Russia's gas monopoly Gazprom accused Ukraine of stealing gas destined for the West when it cut off supplies to its ex-Soviet neighbour over failure to agree a new contract.
The two sides finally agreed on a new contract on January 4. But yesterday Gazprom came close to accusing Ukraine of again stealing Russian transit gas.
"We can call it gas shrinkage, off-take, legal or illegal, whatever. But what is happening in reality is that gas is being held by Ukraine above agreed levels, which is not allowing us to fully meet our obligations with international buyers," Gazprom's export chief Alexander Medvedev said on state RTR television.
"We can't work like that." Gazprom supplies one quarter of Europe's gas needs and several of its clients, including in Italy and Hungary, have complained about reduced supplies over the past week.
Some members of the European Union had severely criticised Moscow for the cuts early this month. But they have refrained from doing so over the past week when Moscow was mainly blaming extreme cold at home and soaring demand in Europe for gas shortages across the continent.
Ukrainian Prime Minister Yuri Yekhanurov told reporters his government was fully meeting obligations on Russian gas transit to Europe.
"We will do everything to cut our domestic consumption. Yesterday Ukraine consumed 407 million cubic metres of gas and our Russian partners are nervous because of it," he added.
"I am grateful to Gazprom for their understanding of this situation caused by a considerable drop in temperatures and that it allowed to increase daily consumption limits for Ukraine," said Mr Yekhanurov.
Ukraine was using around 280 million cubic metres a day at the start of the year, when temperatures were much milder.
With temperatures well below -20°C in Moscow and Kiev and with an even deeper freeze in Gazprom's Siberian heartland, the gas firm's ability to keep its clients satisfied has been tested over the past week.
Many observers have said a second large disruption in European gas supplies in less than a month is highlighting the continent's risks of heavily relying on one major supplier.