(Bloomberg) -- The threat of a nuclear accident persists amid Russia’s invasion, now into its 22nd month, the Ukrainian energy ministry said after a blackout at the Kremlin-occupied Zaporizhzhia facility. 

The nuclear worries are running parallel to stepped-up Russian offensive efforts in Ukraine’s east, including the unconfirmed capture of Mariinka in eastern Donetsk - and as President Volodymyr Zelenskiy calls for extensive fortification in key battleground areas and along Ukraine’s borders with Russia and Belarus.

The Zaporizhzhia nuclear power plant, which was captured by Kremlin forces days after Russia’s full-scale invasion, was completely cut off from electricity overnight, the ministry said Saturday. 

The power network that connects Zaporizhzhia to Ukraine’s power grid was damaged, and the facility used diesel generators to keep working until repairs were made. It was the eighth blackout that the Zaporizhzhia NPP has faced since the start of the war. 

The United Nations’ nuclear safety watchdog, the International Atomic Energy Agency, confirmed the temporary outage in a post on X, formerly Twitter.

Such issues amplify the risks of a nuclear accident, as Russian troops that occupy the plant in southeastern Ukraine aren’t using its equipment properly, the ministry said in an emailed statement.   

The IAEA has warned repeatedly of the risks surrounding the atomic plant, Europe’s largest, located in an active war zone. 

In a statement on Wednesday, the agency cautioned not just about Zaporizhzhia but also the Khmelnytskyi nuclear power plant in western Ukraine, where an IAEA monitoring team “reported hearing several explosions in close proximity.” 

“All of Ukraine’s nuclear facilities remain vulnerable, either directly if hit by a missile or indirectly if their off-site power supplies are disrupted,” said IAEA Director-General Rafael Mariano Grossi. 

Some Russian military bloggers claimed Friday that Kremlin forces had captured Mariinka in eastern Donetsk. That town and nearby Avdiivka have seen fighting for months, but greatly increased Russian attacks over recent weeks weeks. 

Zelenskiy and top commanders discussed the “course of defense operations” in Avdiivka and Mariinka earlier in the week. 

Ukraine’s leader this week ordered an extensive network of fortifications built to hold back Russian forces, as the nation’s summer and autumn counteroffensive yielded limited gains.  

“In all major sectors, we need to boost and accelerate the construction of structures,” Zelenskiy said in his nightly video message on Thursday, after spending the day visiting command posts. “We need to dig in.” 

As well as the east and northeast, fortifications should be built in the Kyiv region and in areas that border Russia and Belarus, Zelenskiy said.  

Zelenskiy and Ukrainian Commander-in-Chief General Valeriy Zaluzhnyi “signaled intent to increase Ukrainian defenses and fortifications around the Ukrainian theater, but notably did not include Zaporizhzhia oblast in discussions of ongoing and future defensive measures,” said analysts at the Institute for the Study of War in the US. 

Ukraine’s military leader also spoke in recent days with General Charles Brown, chairman of the US Joint Chiefs of Staff, to discuss Russian offensive operations, Zaluzhnyi posted on Telegram. 

(Recasts with Zelenskiy comments from second paragraph.)

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