Russia unleashed a massive missile barrage targeting energy infrastructure across Ukraine early Thursday, hitting residential buildings and killing at least five people in the largest scale such attack in three weeks, officials said.

Four people were killed in the Lviv region after a missile struck a residential area, Lviv Gov. Maksym Kozytskyi said. Three buildings were destroyed by fire after the strike and rescue workers were combing through rubble looking for more possible victims, he said.

A fifth person was killed and two others wounded in multiple strikes in the Dnipropetrovsk region that targeted its energy infrastructure and industrial facilities, Gov. Serhii Lysak said.

Air raid sirens wailed through the night across Ukraine, including the capital, Kyiv, where explosions occurred in two western areas of the city. Defense systems were activated around the country, and it wasn't clear how many missiles struck targets or were intercepted.

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The city's administration said Kyiv was attacked with both missiles and exploding drones and that many were intercepted but that its energy infrastructure was hit.

Kyiv Mayor Vitali Klitschko said explosions were reported in the Holosiivskyi district of the city, and two people were wounded in the Sviatoshynskyi district, also on the west side of the city, and cars were ablaze there, the mayor added.

The alarm in Kyiv was lifted just before 8 a.m., with the air raid sirens falling silent after some seven hours.

The missile barrage struck as Russia pushed its advance in Ukraine's eastern stronghold of Bakhmut, where a grinding fight between the two sides has gone on for six months and reduced the city to a smoldering wasteland.

It also came hours after U.N. Secretary-General Antonio Guterres visited Kyiv for talks with President Volodymyr Zelenskyy on extending an agreement that allows Ukraine to ship grain from its Black Sea ports and permits Russia to export food and fertilizers.

In eastern Ukraine, 15 missiles struck Kharkiv and the outlying northeastern region, hitting residential buildings, according to Kharkiv Governor Oleh Syniehubov. He promised to reveal more details about the scale of the damage or any casualties in Ukraine's second-largest city.

"Objects of critical infrastructure are again in the crosshairs of the occupants," he said in a Telegram post.

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Kharkiv Mayor Ihor Terekhov reported on Telegram that there were "problems with electricity" in some parts of the city.

The governor of the southern Odesa region, Maksym Marchenko, also reported strikes on Odesa, saying that energy facilities and residential buildings were hit. Marchenko warned on Telegram for people to stay in shelters.

The Zaporizhzhia Nuclear Power Plant, which is occupied by Russian forces, lost power as a result of the missile attacks, according to nuclear state operator Energoatom.

It was the sixth time the plant was in a state of blackout since it was taken over by Russia months ago, forcing it to rely on 18 diesel generators that can run the station for 10 days, Energoatom said. Nuclear plants need constant power to run cooling systems and avoid a meltdown.

"The countdown has begun," Energoatom said.

Ukraine's Energy Minister Herman Halushchenko condemned the missile strikes as "another barbaric massive attack on the energy infrastructure of Ukraine," saying in a Facebook post that facilities in Kyiv, Mykolaiv, Kharkiv, Zaporizhzhia, Odesa, Dnipropetrovsk and Zhytomyr regions had been targeted.

Ukrainian Railways reported power outages in certain areas, with 15 trains delayed up to an hour.

Preventive emergency power cuts were applied in Kyiv, Dnipropetrovsk, Donetsk and Odesa regions, supplier DTEK said. Klitschko said 40% of consumers in Kyiv were without heating because of the emergency power cuts. Water supplies were uninterrupted, he said.

More explosions were reported in the northern city of Chernihiv and the western Lviv region, as well as in the cities of Dnipro, Lutsk and Rivne. Ukrainian media also report explosions in the western regions of Ivano-Frankivsk and Ternopil.

Russia has been hitting Ukraine with these massive missile attacks since last October. Initially, the barrages targeting the country's energy infrastructure took place weekly, plunging the entire cities into darkness, but became more spread out in time, with commentators speculating that Moscow may be saving up ammunition.

The last massive barrage took place on Feb. 16.