Russia in June halted gas exports to Ukraine after Kiev balked at paying higher prices that Moscow demanded in the wake of the February ouster of a Kremlin-backed president.
Ukraine last year imported half of the gas it consumed from Russia. It is currently trying to make up for the difference by boosting imports from its western European allies.
Ukrainian Energy Minister Yuriy Prodan said the conflict-torn country will probably soon encounter severe energy shortages despite efforts to diversify its gas supply base.
He accused Russia of "using gas as a political tool" and reported a shortage of gas in the country's underground storage tanks.
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Poland said today it had resumed its so-called "reverse flow" gas deliveries to Ukraine after a brief interruption it blamed on an unexplained cut in Russian supplies.
But its daily shipment of four million cubic metres accounts for just three percent of the gas Ukraine consumed last year.
The chief executive of DTEK -- an energy holding owned by powerful tycoon Rinat Akhmetov -- said Ukraine will have to import both coal and electricity from Russia this winter because of a work stoppage in the region's mines.
"We have no choice but to start importing electricity from Russia. We are dependent on Russia not only in gas supplies, but also coal and electricity," Maksym Tymchenko said.