MOSCOW - A backup power line supplying the Russian-occupied Zaporizhzhia nuclear power plant in Ukraine has gone down, the Russian-controlled management of the plant said on Thursday.

Ukraine's state-run nuclear power company, Energoatom, said the main 750 kilovolt (kV) power line, recently restored by Ukrainian engineers, was still running.

The six reactors at the Zaporizhzhia plant, held by Russia and located close to the front line of the war in Ukraine, are not in operation but it relies on external power to keep its nuclear material cool and prevent a catastrophic accident.

The Russian management said on Telegram that the reasons for the outage, which had not caused any change in the radiation level, were being investigated.

It said the problem was with the 330 kV "Ferosplavnaya" power line. This is a backup which, according to the International Atomic Energy Agency (IAEA), was restored in the middle of last month after an outage of more than three weeks.

The main 750 kV "Dniprovska" power line went down for almost five hours on March 22, highlighting what the IAEA said were "ever present dangers to nuclear safety and security" from the Russia-Ukraine war.

Russia and Ukraine have each accused the other at various times of shelling the Zaporizhzhia plant, which is Europe's largest.

According to the IAEA, the plant has suffered eight instances of complete loss of off-site power in the past 19 months, forcing it to rely on emergency diesel generators. REUTERS