KIEV (Reuters) - Ukraine's energy minister said on Monday Russia had suspended coal supplies to Ukraine, a blow to domestic energy suppliers who are struggling with a severe lack of raw fuel for power plants due to a separatist conflict in the industrial east.

On Nov. 12 Prodan said Ukraine would have to rely on Russian coal to get through the winter after the war in the east disrupted supplies to thermal power plants (TPP), which provide around 40 percent of the country's electricity, and left reserves critically low ahead of the cold season.

"According to information received from DTEK and (state-run) Tsentrenergo, coal supplies from Russia have been suspended," an energy ministry spokesman quoted Prodan as saying.

Ukraine's biggest private energy company DTEK said the suspension of supplies was unexpected.

"The company received no official notification about the delay in shipments. Now we are trying to find out the reasons and circumstances of the current situation," DTEK said in a statement.

DTEK, part of the business empire of Ukrainian tycoon Rinat Akhmetov, said it had imported a total of 1.3 million tonnes of coal from Russia since August.

Ukraine, which needs to import around 1 million tonnes of coal per month to meet its electricity needs, signed a supply deal with South Africa to boost reserves, but earlier this month the supplier discontinued shipments, citing concerns about political instability.

Ukraine's reliance on Russian coal is a serious setback to the country's efforts to lessen energy dependence on its powerful neighbor.

Kiev's relations with the Kremlin are at an all-time low following Russia's annexation of Ukraine's Crimea peninsula and its involvement in the eastern conflict in which over 4,300 have been killed.

(Reporting by Pavel Polityuk; Additional reporting by Damir Khalmetov; Writing by Alessandra Prentice, editing by William Hardy and Susan Thomas)