Ukraine will be forced to implement more power cuts if the weather gets sharply colder, Prime Minister Arseny Yatseniuk said on Wednesday.
Kyiv had already temporarily cut off electricity to Crimea.
Ukraine used to be self-sufficient in electricity, but months of fighting a pro-Russian uprising has disrupted coal supplies to thermal power plants, which had generated around 40 percent of its power.
“At the moment the warm weather is saving us,” Yatseniuk said in a government meeting.
“If temperatures go down, this means coal consumption will rise and the rolling blackouts will increase significantly.”
The energy ministry temporarily cut off power supplies to Crimea after the peninsula, annexed by Russia, failed to curb consumption as required by all regions due to the power shortage.
Supplies were later resumed, but Energy Minister Voldymyr Demchyshyn warned that all regions, including rebel-held territories, would be cut off entirely if they did not ration power according to the official guidelines.
“The outlined limits will be monitored very strictly,” he told the government.
Kyiv stopped paying pensions and social benefits in Donetsk and Luhansk out of worries the funds would end up in rebel hands, but said in November it would continue supplying gas and electricity.
Coal reserves stand at 1.5 million tons compared with normal winter stocks of 4-5 million tons, according to energy ministry data.
Ukraine has looked to buy in coal from abroad to restock depleted reserves, but potential supplies from Russia have been held up at the border.
Demchyshyn said he was holding talks with Russia's energy ministry and hoped that an agreement would be reached “in the near future” that would allow the more than 1,000 freight cars at the border to cross into Ukraine.
He also said talks on power imports from Russia were in progress.
Turning to Russia for supplies will be a blow for Kyiv, whose relations with the Kremlin are at an all-time low following Russia's annexation of Crimea in March and its involvement in the eastern conflict in which over 4,700 have been killed.