Updated November 23, 2022 at 10:42 AM ET

KYIV, Ukraine — Russian airstrikes on Ukrainian cities Wednesday knocked out power and water service and caused at least six civilian deaths in the latest assault on the country's struggling energy grid, Ukrainian authorities said.

Also, Ukraine intentionally disconnected three nuclear power plants from the national electricity grid as a precautionary measure in response to the Russian strikes, the energy company Ukrenergo said.

And in neighboring Moldova, which is connected to Ukraine's power network, more than half the country lost power, Moldovan leaders said.

Ukraine's capital Kyiv, the western city of Lviv and the southern city of Mykolaiv were among multiple areas reporting missile strikes.

At least six people were killed and more than 30 injured around the country, according to the national police.

Kyiv Mayor Vitali Klitschko said on the Telegram messaging app "one of the capital's infrastructure facilities has been hit." He said running water has been cut off due to shelling throughout the city, and a 17-year-old girl was among those killed.

Klitschko also said 21 of the 31 missiles targeted at Kyiv were shot down. This could not be independently verified, but the Ukrainians say they've been shooting down roughly two-thirds to three-quarters of the incoming Russian missiles.

However, the missiles and drones that do reach their target have put the country's energy system in jeopardy.

"More cruel missile strikes across the country as Russia tries to punish Ukraine for daring to be free," the U.S. ambassador to Ukraine, Bridget Brink, said in a tweet. "Russia's attempt to dominate Ukraine by plunging it into the cold and dark will fail."

In a statement, the energy company Ukrenergo said that the three nuclear power plants — Rivne, South Ukraine and Khmelnytskyi — were disconnected from the grid as a safety measure.

After a brief emergency shutdown, the nuclear reactors have been turned back on, but were still not reconnected to the national grid, the company added.

The Russians are in control of a fourth nuclear plant, Zaporizhzhia, which came under shelling on Sunday.

In the west of the country, one regional administrator, Serhii Hamalii, said on Telegram that most of the surrounding area was without power and water due to the Russian attacks. This led to the Khmelnytskyi nuclear power station being taken offline.

In the southern region of Mykolaiv, the military administrator, Vitaliy Kim, also said the nuclear plant in his area has been cut from the grid, leading to a risky shutdown of the reactors there.

Ukrainian officials stress that the power cuts have the cascading effect of turning off the heat and water in many cases. And with temperatures often below freezing, the water in pipes could freeze, adding further complications.

In Moldova, President Maia Sandu wrote this about Russia on Facebook: "We can't trust a regime that leaves us in the dark and cold, that purposely kills people for the mere desire to keep other peoples poor and humble."

Russia has been unleashing large-scale strikes on Ukraine's power systems since Oct. 10 in an effort to cut off power to civilians as the country heads into winter.

Ukraine is scrambling to prepare for the winter. In a Tuesday night video address, President Volodymyr Zelenskyy said there are now 4,000 centers to take care of civilians if there are extended power cuts.

He called them "points of invincibility," saying they will provide heat, water, phone charging and internet access. Many will be in schools and government buildings.

"All of us must be prepared for any scenario," he said. "By helping each other, we will all be able to get through this winter together."

Julian Hayda and Ashley Westerman contributed to this story from Kyiv.

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