Russia has repeatedly targeted Ukraine's energy infrastructure in recent weeks.
Kyiv was left without water and electricity after new Russian strikes caused power outages across Ukraine and neighbouring Moldova.
Missile strikes hit an "infrastructure" site in Ukraine's capital, according to mayor Vitali Klitschko.
A series of explosions and anti-aircraft sirens were heard in the city and several other areas of the country on Wednesday afternoon.
"One of the capital's infrastructures was hit. Stay in shelters," Klitschko wrote on Telegram, adding that water supplies had been suspended.
"Several other explosions in various neighbourhoods," he said. "Rescue services and doctors are on their way to the affected places."
Kyiv's regional administration has claimed that at least three people were killed and six others injured after a two-story building was struck by rockets.
Authorities in Lviv, western Ukraine, also reported that the "whole city" was without electricity after fresh Russian rocket attacks.
Two Russian missile strikes hit an electricity substation causing power cuts in two districts, according to regional governor Maxim Kozytsky.
"There may be interruptions in water supply," mayor Andriy Sadovy added on Telegram.
Three Ukrainian nuclear power plants were "disconnected" from the electricity grid on Wednesday amid massive power outages, national operator Energoatom said.
Half of Moldova had also suffered "massive power outages" on Wednesday, Deputy Prime Minister Andrei Spinu said on Wednesday.
"As a result of Russia's bombing of Ukraine's energy system over the past hour, we have massive power outages throughout the country," Spinu wrote on Facebook.
Russia has repeatedly fired on Ukraine's infrastructure in recent weeks, leaving up to 10 million people without electricity, but has denied hitting civilian targets.
The latest reported strikes come after three people -- including a newborn baby -- were allegedly killed by Russian strikes on Zaporizhzhia and Kharkiv.
Ukrainian President Volodymyr Zelenskyy has accused Moscow of "terror" and "murder".
"Russia must be isolated at all levels and held accountable in order to put an end to its long-standing terrorist policy in Ukraine and throughout the world," he said on Wednesday.
The European Parliament voted to declare Russia a "state sponsor of terrorism," nine months after the invasion began on February 24.