Ukrainian refugees should not return until spring to help ease pressure on the energy system after a wave of Russian attacks, the government said.
"The networks will not cope," said Deputy Prime Minister Iryna Vereshchuk.
Ukrainian President Volodymyr Zelensky said Russian air strikes had destroyed more than a third of the country's energy sector.
Russia said it began attacking Ukraine's energy networks in retaliation for an attack on a bridge linking mainland Russia to occupied Crimea, although Kyiv has not said it was behind the bridge attack.
