Ukrainian engineers have managed to restore back-up power to the Zaporizhzhia Nuclear Power Plant (ZNPP), a much-needed development after the plant twice over the past week lost all access to external electricity, Director General Rafael Mariano Grossi of the International Atomic Energy Agency (IAEA) has said.

"The availability of back-up off-site electricity through the switchyard of the nearby thermal power station provides Europe's largest nuclear power plant with a buffer if the connection to its last remaining operating 750 kilovolt (kV) power line were to be cut again," Grossi, quoted in the update on Ukraine on the agency's website late on Friday, said.

According to the update, in recent days, two of the ZNPP's back-up power lines – connecting it to the thermal power plant switchyards – have been repaired.

"Working in very challenging conditions, operating staff at the Zaporizhzhia Nuclear Power Plant are doing everything they can to bolster its fragile off-site power situation. Restoring the back-up power connection is a positive step in this regard, even though the overall nuclear safety and security situation remains precarious," Grossi said.

The IAEA said that before the conflict, the ZNPP had access to the grid through four high-voltage power lines, but three of them have fallen victim to the fighting. The back-up power lines – offering indirect access to the electricity grid – had also been down in recent weeks.

At the same time, The IAEA team also said further preparatory activities to restart reactor unit 5 were continuing, and that work to also restart unit 6 was expected to get under way on October 15.

Separately, the ZNPP has received additional fuel supplies for its 20 diesel generators, following the arrival of seven trucks, of which five recently came from the city of Zaporizhzhia, and two earlier from Russian-controlled territory, the IAEA team said.

The plant currently has fuel for at least ten days operation of diesel should external power be lost, the IAEA said.

The director general of the agency in recent weeks was engaged in high-level consultations with Ukraine and Russia aimed at agreeing and implementing a nuclear safety and security protection zone around the ZNPP as soon as possible, stressing it is urgently needed to help prevent a nuclear accident.

"The consultations are progressing," the IAEA said.