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.

The United States announced an additional $2 billion military aid package for Ukraine on Friday, as the Eastern European country marks the one-year anniversary of Russia's full-scale invasion.

The new aid package includes more missiles for Ukraine's U.S.-supplied High Mobility Artillery Rocket Systems (HIMARS), additional 155mm artillery ammunition, more Switchblade one-way drones and other military equipment, according to the U.S. Department of Defense.

"One year into a war of aggression waged by a permanent member of the U.N. Security Council, our allies and partners worldwide stand united and resolute," U.S. Secretary of Defense Lloyd Austin said in a statement. "Putin's reckless, illegal war is not just an all-out assault on Ukraine's sovereignty and a historic threat to European security. It is also a direct attack on the system of rules, institutions, and laws that the world built at such great cost after World War II -- a system that rejects aggression and respects the rights of all countries, big and small."

The additional aid is being provided under the Ukraine Security Assistance Initiative (USAI) plan, meaning this equipment and artillery have to be made from scratch before being delivered, which will take time. This is different from the other aid packages that come from existing U.S. military stockpiles and get delivered faster.

With the new aid package, the Biden administration has now provided $31.8 billion in assistance to Ukraine since Russia's war began on Feb. 24, 2022.

"Putin thought that Ukraine’s defenses would collapse, that America's resolve would falter, and that the world would look the other way. He was wrong," Lloyd said. "One year later, Ukraine's brave defenders have not wavered, and neither has our commitment to support them for as long as it takes. Despite the Kremlin's campaign of cruelty, the people of Ukraine have shown stunning bravery, skill, and fortitude. Today and every day, we stand by the courageous Ukrainians fighting to defend their country, and we mourn with those who have lost their loved ones in Moscow's monstrous and unnecessary war."

"Difficult times may lie ahead, but let us remain clear-eyed about what is at stake in Ukraine," he added. "And let us remain united in purpose and in action -- and steadfast in our commitment to ensure that a world of rules and rights is not replaced by one of tyranny and turmoil."

-ABC News' Luis Martinez