Power has been cut off from the former nuclear power plant at Chernobyl, Ukraine’s state energy company has said.
Ukrenergo blamed the outage on actions by Russian troops who seized Chernobyl nearly two weeks ago.
The company said the conflict meant it could not restore power at Chernobyl – site of the world’s worst nuclear accident in 1986.
The head of the UN nuclear watchdog said the outage did not impact safety.
Although no longer a working power station, Chernobyl was never fully abandoned and still requires constant management.
Spent nuclear fuel is cooled at the site.
Rafael Grossi, director-general of the UN watchdog, the International Atomic Energy Agency (IAEA), said that even without an electrical supply, the spent nuclear fuel would not heat up sufficiently to cause an accident.
The acting head of the Chernobyl nuclear plant, Valeriy Seyda said the generators had enough fuel to power the site for 48 hours.
The IAEA said it was concerned about staff at the site working under Russian guard who had in effect been stuck there for 14 days, with no prospect of relief by co-workers.
Ukraine’s energy minister, German Galushchenko, said the staff would now be “mentally exhausted”, adding that protecting Ukraine’s nuclear plants should be a priority “for the EU, the world, and not just for Ukraine”.