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.
The Republican-controlled US Senate passed President Donald Trump's tax and spending bill on Tuesday, signing off on a massive package that would enshrine many of his top domestic priorities into law while adding $3.3 trillion to the national debt.
More than a thousand schools were closed in France on Tuesday and the top floor of the Eiffel Tower was shut to tourists as a severe heatwave continued to grip Europe, triggering health alerts across the region.
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