Electricity supply has been fully restored in Kyiv after Russia's overnight barrage of missile attacks on Ukraine, Kyiv Mayor Vitaliy Klitschko said in a Telegram post Thursday.

Also, the Zaporizhzhia nuclear power plant is now "receiving electricity for its own needs from the Ukrainian grid after power supply was cut," Russian news agency Interfax reported.

-ABC News' Tatiana Rymarenko and Natalia Shumskaia

Russia's overnight barrage of missiles aimed at civilian infrastructure may have knocked heat out to as much as 40% of Ukrainians, the White House said on Thursday.

Russian President Vladimir Putin is attempting to "brutalize" the people of Ukraine, John Kirby, spokesperson for the White House National Security Council, told ABC News' George Stephanopoulos on "Good Morning America" on Thursday.

"It also appears, George, that they were definitely targeting civilian infrastructure," Kirby said. "I would agree with the Ukrainians. He's just trying to brutalize the Ukrainian people"

Russian forces early on Thursday launched 81 missiles from land and sea, Ukrainian officials said. Eight uncrewed drones were also launched in what officials described as a "massive" attack.

Eleven regions and cities were targeted in an attack that lasted at least seven hours, officials said.

Kirby said on Thursday that the White House expects to see more fighting on the ground in Ukraine for at least the "next four to six months."

"We know that the Russians are attempting to conduct more offensive operations here when the weather gets better," he said.

Ukrainian President Volodymyr Zelenskyy on Thursday said Russian officials had returned "to their miserable tactics" as they launched at least 81 missiles at Ukrainian sites overnight.

"The occupiers can only terrorize civilians. That's all they can do. But it won't help them," he said on Telegram. "They won't avoid responsibility for everything they have done."

He added, "We thank the guardians of our skies and everyone who helps to overcome the consequences of the occupiers' sneaking attacks!"

-ABC News' Yulia Drozd and Joe Simonetti

Waves of missiles and a handful of drones were launched overnight by Russia, targeting energy infrastructure and cities across Ukraine, officials said.

The attack on "critical infrastructure" and civilian targets lasted throughout the night, Verkovna Rada, Ukraine's parliament, said on Twitter. Energy was being gradually restored on Thursday morning, the body said.

Ukraine's parliament and military said at least 81 missiles were fired from several bases. Eight Iranian-made drones were also launched, the military said.

Ukraine destroyed 34 cruise missiles and four drones, military officials said on Facebook.

"Russia's threats only encourage partners to provide long-term assistance to Ukraine," said Yehor Chernev, deputy chairman of the Committee on National Security, Defense and Intelligence.

Russia "will be sentenced as a terrorist state" for its attacks, Ruslan Stefanchuk, Rada's chairperson, said on Twitter.

Russia plans to move tactical nuclear weapons in Belarus to the country's western borders, Boris Gryzlov, the Russian ambassador to Belarus, said Sunday.

Gryzlov's announcement comes just three days after Russia and the United States clashed in the United Nations over the Kremlin's plans to deploy tactical nuclear weapons in Belarus. U.S. officials denounced the move as a desperate attempt by Russia to avoid military defeat and “threaten the world with nuclear apocalypse."

Gryzlov said in an address aired on the Belarusian STV channel that tactical nuclear weapons "will be moved to the western borders of our Union State and will increase the possibilities for ensuring our security."

The western border of Belarus is shared by Poland, a NATO country supporting Ukraine. Russian forces have used Belarus as a staging ground for the war in Ukraine.

"This will be done despite the noise in Europe and the United States," Gryzlov said.

Ukrainian President Volodymyr Zelenskyy condemned the decision and slammed Belarusian President Alexander Lukashenko, saying he "no longer decides which weapons are on his territory."

"And does (Vladimir) Putin threaten the world? Of course, if Ukraine does not resist, it will fall, Putin will move on, we have emphasized this many times," Zelenskyy said. "With the help of our friends and partners, our army will stand firm and win what is rightfully ours. Victory and our independence."

-ABC News' Will Gretsky