Ukraine introduced emergency power cuts in six regions amid what authorities described as a "massive" Russian missile strike, the national grid operator said on Wednesday.
Kyiv's air force had warned of numerous groups of missiles launched by Russia amid a nationwide air-raid alert, but there were no immediate reports of damage.
In a statement, Ukrenergo said it had introduced the power cuts in the Kharkiv, Sumy, Poltava, Zaporizhzhia, Dnipropetrovsk and Kirovohrad regions.
Separately, Ukrainian energy minister German Galushchenko said on social media that "preventative measures" involving the distribution system were also in force.
Russia has carried out regular air strikes on Ukraine's energy grid as its ground forces press ahead on the battlefield in the Kremlin's three-year-old invasion.
Israeli Prime Minister Benjamin Netanyahu said the ceasefire in Gaza would end and the military would resume fighting Hamas until it was defeated if the Palestinian group did not release hostages by midday Saturday.
The United Nations said on Tuesday that one of its staff members had died in detention in northern Yemen, where the UN has repeatedly called for the Houthi movement to free detained UN employees.
Government offices, schools and workplaces fell silent in Sweden at midday on Tuesday in remembrance of the victims of a mass shooting at an adult education centre last week when a gunman killed 10 people before turning his weapon on himself.
UN Secretary-General Antonio Guterres urged Hamas to continue with the planned release of hostages on Tuesday, a day after the group announced its intention to halt the exchange.
US President Donald Trump substantially raised tariffs on steel and aluminum imports to a flat 25 per cent "without exceptions or exemptions" in a move to aid the struggling industries but which increases the risk of a multi-front trade war.