The International Atomic Energy Agency says a back-up power line to the Zaporizhzhia nuclear power plant in southern Ukraine has been disconnected due to damage caused by shelling.

The IAEA said in a statement on Friday that the connection to the plant's last functioning back-up line was lost on Thursday as a result of damage on the other side of the Dnipro River, some distance away from the plant itself.

The statement did not blame either Russia or Ukraine for the shelling.

The nuclear watchdog said work to repair the line is already underway.

It added that the Zaporizhzhia plant continues to receive the electricity it needs for reactor cooling and other essential functions from the facility's only remaining operational external power line.

The site of one of Europe's largest nuclear power stations has been occupied by Russian forces since the early stages of the invasion of Ukraine.

Workers have had to restore external power to the plant every time shelling cut the supply line.

IAEA Director General Rafael Grossi said all military action potentially threatening the nuclear safety and security of Ukraine's nuclear power plants must stop immediately.

He stressed the need to implement a nuclear safety and security protection zone around the Zaporizhzhia plant as soon as possible.