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.

After some missed calls, President Joe Biden finally connected with the parents of Wall Street Journal reporter Evan Gershkovich, White House press secretary Karine Jean-Pierre confirmed Tuesday.

"He felt it was really important to connect with Evan's family," she told reporters on Air Force One as the president travels to Ireland.

Meanwhile, National Security Council spokesperson John Kirby said Gershkovich's detention is "pretty fresh" and officials are still trying to get consular access to Gershkovich, which they have not been able to do.

He would not get into any specific conversations the U.S. is having with Russians about releasing Gershkovich or if a prisoner swap is a possibility.

"I just want to make a couple of things clear that is, the determination of wrongful detention, it doesn't start the clock necessarily on communicating with the Russians about getting him released," Kirby said. "We're very early in this process here and I certainly, I think you can understand why I wouldn't talk about any discussions we might be having with the Russians about his release or Paul [Whelan]'s release. We certainly wouldn't do that."

Kirby said the administration is "certainly having discussions about what we can do to get him released."

"I don't want to go into details about these internal deliberations, having things out in the public sphere viscerally might actually make it harder to get Evan and Paul home, and that's what we're focused on," Kirby said.

-ABC News' Justin Gomez