A "massive" Russian missile attack on at least six cities across Ukraine killed at least two people and left more than 20 others wounded Thursday night, Ukrainian officials said. Ukrenergo, the country's electrical grid operator, said on social media that the missile barrage was Russia's first successful attack targeting energy facilities in months, and it reported partial blackouts in five different regions across the country.

"Tonight, Russia launched a massive attack on Ukraine," deputy head of Ukraine's presidential office Oleksiy Kuleba said, warning that "difficult months are ahead" for the country as "Russia will attack energy and critically important facilities."

The strike came as Ukraine's frigid winter months approach and just hours after Ukrainian President Volodymyr Zelenskyy cautioned at the United Nations General Assembly that Russian leader Vladimir Putin was not afraid of weaponizing nuclear power.

• Political divide emerges on Ukraine aid as Zelenskyy heads to D.C.

Zelenskyy warned from the U.N. podium that if Russia is allowed to win the war in Ukraine, other countries will be next. 

"The mass destruction is gaining momentum," he said. "The aggressor is weaponizing many other things and those things are used not only against our country, but against all of yours as well."

One of those weapons, Zelenskyy said, is nuclear energy, and the greatest threat is at the sprawling Zaporizhzhia Nuclear Power Plant in southern Ukraine, which has been occupied by Russian forces for more than a year.

For several months, Ukraine's counteroffensive has been partly focused on liberating territory around the facility, amid fear that Moscow could deliberately cause a radiation leak there to use as a false pretext for further aggression.

For 18 months, the ground around the massive complex, and even Europe's largest nuclear power plant itself, has repeatedly been targeted in missile and drone attacks. The clashes around the sensitive site have drawn dire warnings from the United Nations nuclear energy watchdog as engineers have had to regularly take its six reactors offline and rely on backup power to keep the plant safely cooled.

Ukraine remains heavily dependent on nuclear energy. It has three other plants still under its direct control which, combined, power more than half the country. That makes them too important to shut down, despite the risks of Russian attacks.

But until now, only Moscow was capable of providing fuel for Ukraine's Soviet-era nuclear reactors. So, as part of a wider strategy by Kyiv to sever any reliance on Russia, Ukraine partnered with the Pittsburgh-based company Westinghouse to develop its own fueling systems to power its plants. The first such system was installed this month at the Rivne plant.

The plant is now being fired by fuel produced at a Westinghouse plant in Sweden. 

Ukraine's Minster of Energy, Hermann Galuschenko, told CBS News it's a shift that was a long time coming. He said it gave him pride to see nuclear fuel being fed in to power the reactors recently at the Rivne plant for the first time under the new system.

"I'm proud that even during the war, we managed to do some historical things," he said. "We should get rid of Russian technologies in nuclear."

Ukraine is still haunted by the 1986 nuclear disaster at Chernobyl. One of the worst man-made catastrophes in history, the Chernobyl meltdown left millions of acres of forest and farmland contaminated and caused devastating long-term health problems for thousands of people in the region.

As Ukrainian forces battle to push Russia out of Zaporizhzhia, the lingering fear is that the Kremlin could be preparing to sabotage that nuclear power plant with mines or other military explosives.

In:
• War
• Nuclear Power Plant
• Ukraine
• Russia
• United Nations
• Nuclear Attack
• Vladimir Putin
• Volodymyr Zelenskyy

Imtiaz Tyab

Imtiaz Tyab is a CBS News correspondent based in London.

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