KYIV, Ukraine — Russia unleashed "a massive rocket attack" that hit critical infrastructure and residential buildings in 10 regions of Ukraine, the country's president said Thursday, with officials reporting at least six deaths in the largest such night-time attack in three weeks.

Volodymyr Zelenskyy described the barrage that came while many people slept as an attempt by Moscow "to intimidate Ukrainians again."

"The occupiers can only terrorize civilians. That's all they can do," Zelenskyy in an online statement.

The war has largely ground to a battlefield stalemate over the winter. The Kremlin's forces started targeting Ukraine's power supply last October in an apparent attempt to demoralize the civilian population. The barrages later became less frequent, with analysts speculating Russia may have been running low on ammunition. The last massive barrage took place on Feb. 16.

The latest attack left almost half of consumers in Kyiv without heating, with temperatures at around 9 degrees Celsius (48 Fahrenheit) amid a spring thaw.

In southern Ukraine, 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 is the sixth time the plant has been 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.

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.

Overall, Russia launched 81 missiles and eight exploding Shahed drones, according to Ukraine's Chief Commander of the Armed Forces Valerii Zaluzhnyi. Thirty-four cruise missiles were intercepted, as were four drones, he said.

Viktor Bukhta, a 57-year-old resident of a damaged residential building in Kyiv's Sviatoshynski district, where officials said three people were wounded and apartment windows were shattered, said a missile landed nearby at about 6.45 a.m..

"We went into the yard. People were injured, they helped, first aid kits were handed out from the cars," he told The Associated Press. "Then the cars caught fire. We tried to extinguish them with car fire extinguishers. And I got a little burnt."

Kyiv's city administration said the capital was attacked with both missiles and exploding drones. Many were intercepted but its energy infrastructure was hit.

Smoke could be seen rising from a facility in Kyiv's Holosiivskyi district and police had cordoned off all roads leading to it.

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

Private electricity operator DTEK reported that three of its power stations had been hit. There were no casualties, but the company said equipment was severely damaged.

Kharkiv, Ukraine's second-largest city, was left without running water and heating after 15 missiles hit the region, mayor Ihor Terekhov told the Ukrainian public broadcaster.

Terekhov added that electricity shortages also disrupted mobile communications and public transport in the city, as all trams and trolleybuses ground to a halt.

Five 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, and rescue workers were combing through rubble looking for more possible victims, he said.

A sixth 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.

In the south, Odesa Gov. Maksym Marchenko said residential buildings were hit and several power lines were damaged in strikes on his region. He said six missiles and one drone were shot down.

Ukrainian 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.

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.

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