Ukraine faces a energy crisis if a blockade on rebel held territory is not lifted.
Activists have cut off the country’s coal supply in the separatist-held area of Donbass.
And the authorities have warned that the move could deprive millions of heating and electricity as well as costing billions of dollars.
Ukrainian President Petro Poroshenko said the blocking of the railway coal link to the east of the country was a “destabilising factor”.
The European Union and the United States chave both called for action to prevent “a major energy crisis”.
An EU spokesman added: “Those responsible for the blockade must cease their actions and the authorities must address this problem as a matter of priority.
Ukraine’s energy industry relies on coal mined in separatist-held territory.
Activists want this to stop as they claim it only fills the pocket of rich oilgarchs and fuels further conflict.
Nearly 10,000 people have been killed since a pro-European uprising in Kiev ousted a Moscow backed president.
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