The southern Ukrainian city of Odesa was left without power on Saturday following a night-time attack by "kamikaze drones" launched by Russia, authorities said.
"As of now, the city is without electricity," Kyrylo Tymoshenko, deputy head of the presidential administration, said on messaging app Telegram.
Only critical infrastructure including hospitals and maternity wards had access to electricity.
"The situation remains difficult, but is under control," Tymoshenko said.
The Black Sea port of Odesa was a favourite holiday destination for many Ukrainians and Russians before President Vladimir Putin sent troops to pro-Western Ukraine on February 24.
Maksym Marchenko,the governor of the region of Odesa, said Russia had attacked the city with "kamikaze drones" overnight.
"As a result of the strike, there is no electricity in almost all districts and communities of our region," he said.
Two drones were shot down by Ukrainian air defence units, Marchenko added.
On Friday, Kyiv said southern regions of the war-scarred country including Odesa were suffering the worst electricity outages days after the latest bout of systematic Russian assaults on the Ukrainian energy grid.
Russia fired dozens of cruise missiles at key infrastructure in Ukraine on Monday, piling pressure on the country's already ailing grid after repeated attacks.
Russia began targeting Ukraine's infrastructure during humiliating military defeats.
On Thursday, President Vladimir Putin vowed to keep battering Ukraine's energy grid despite an outcry against the attacks that have plunged millions into cold and darkness.
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