The site, occupied by Russian forces since March 2022, lost its connection to the grid on September 23 for the 10th time -- the longest outage of external power supply to the facility since Russia invaded Ukraine.

Repairs to the off-site power lines began after the "establishment of local ceasefire zones to allow work to proceed", Rafael Grossi, head of the International Atomic Energy Agency, said in a post on X.

The IAEA said that both sides had worked with the agency to allow the "complex repair plan" to proceed.

"Restoration of off-site power is crucial for nuclear safety and security," it said.

The agency said later it expected the work to take about a week. It had previously said repairs were needed on both sides of the front line, several kilometres from the plant.

Both Russia and Ukraine confirmed the repair works were ongoing.

Since the outage, the largest nuclear power plant in Europe has been powered by backup diesel generators. The IAEA says safety has been maintained with reactors continuing to be effectively cooled.

Located near the city of Enerhodar along the Dnieper River, the nuclear plant is close to the front line.

Its six reactors, which produced about one-fifth of Ukraine's electricity before the war, were shut down after Moscow took control.

However, the plant needs electricity to maintain its cooling and safety systems to prevent a disaster.

At the beginning of October, Moscow claimed that the situation was "under control" in Zaporizhzhia following concerns raised by Ukrainian President Volodymyr Zelensky.

Moscow and Kyiv have repeatedly accused each other of risking a nuclear disaster by attacking the site and have blamed each other for the latest power outage.