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.

As tens of thousands of Russian troops lined up along Ukraine’s eastern and northern borders for "military exercises" last February, some international observers warned that Russia was about to do the unthinkable.

U.S. President Joe Biden had declassified intelligence in the weeks prior that showed an attack on Ukraine's sovereignty was imminent. That intel was shared with allies, in an attempt to rally support and to stop the war, but the effort proved unsuccessful. The invasion began on Feb. 24, 2022.

The following four seasons have seen some of the bloodiest fighting on European soil in generations. Tens of thousands of Russian and Ukrainian troops have been killed. And Ukrainian civilians have been terrorized by missiles aimed at energy infrastructure, city centers and apartment buildings.

This month marks both the 9-year anniversary of Russian President Vladimir Putin's invasion of Ukraine's Crimean Peninsula, which he illegally annexed in 2014, and the first anniversary of his full-scale invasion of Ukraine.

The ends to which he'd go in his mission to capture Ukraine have become clear in the last year.

-ABC News' Kevin Shalvey