Five civilian deaths have been reported, and 40 percent of the residents of Kyiv are without heating in the wake of a huge overnight Russian missile barrage. Ukraine's second-largest city Kharkiv is without power, water or heating.
Pre-dawn Russian strikes targeted energy infrastructure across Ukraine on Thursday, resulting in massive power outages following an attack on Europe's largest nuclear power plant.
Kyiv mayor Vitali Klitschko said 15 percent of households were without power and 40 percent without heating following explosions in two areas of the Ukrainian capital.
Ukraine's second-largest city Kharkiv was left without power, water or heating on Thursday after Russia launched more than 80 cruise missiles at energy facilities across the country.
Ukraine's nuclear energy operator said the strikes had also cut off the electricity supply to the Zaporizhzhia nuclear power plant, which is controlled by Russian forces.
For the sixth time since it was taken over, the facility is now operating on diesel generators which have an autonomy of 10 days.
"The countdown has begun. If it is impossible to renew the external power supply of the station during this time, an accident with radiation consequences for the whole world may occur," Energoatom said.
There were also strikes reported on energy plants in several other parts of Ukraine, including Kharkiv in the northeast and the region of Odesa in the southwest.
In the Kharkiv region, located on the border with Russia, governor Oleg Synegubov said there had been 15 strikes.
Battle for Bakhmut rages
The wave of air strikes comes after Russia reported making gains in the battle for the industrial city of Bakhmut, which has been the focus of months of fierce combat.
Russia's Wagner mercenary group, which has spearheaded the attack on Bakhmut, claimed to have captured the eastern part of the city.
"What we see is that Russia is throwing more troops, more forces and what Russia lacks in quality they try to make up in quantity," Nato Secretary General Jens Stoltenberg told reporters in Stockholm on the sidelines of an EU defence ministers meeting on Wednesday.
"We cannot rule out that Bakhmut may eventually fall in the coming days," the head of the US-led military alliance said, adding that "this does not necessarily reflect any turning point of the war".
Ukrainian officials have warned that the fall of Bakhmut could lead to further Russian advances in eastern Ukraine.
Guterres stresses grain deal
Ukrainian President Volodymyr Zelensky on Wednesday hosted UN chief Antonio Guterres in Kyiv. It was the UN chief's third visit to Ukraine since Russia's invasion.
Guterres stressed the need to extend a deal that has allowed Ukraine to export its grain but is due to expire.
"I want to underscore the critical importance of the rollover of the Black Sea Grain Initiative on 18 March," Guterres said.
At their meeting in Stockholm, the EU defence ministers discussed a plan to rush one billion euros' worth of ammunition to Ukraine as pressure mounts on Kyiv's allies to bolster supplies to the war effort.