Zaporizhzhia nuclear power plant in Ukraine has lost connection to the last remaining main external power line but continues to supply electricity to the grid through a reserve line, the International Atomic Energy Agency (IAEA) said on Saturday.

The UN nuclear watchdog's experts now stationed at the plant were told by Ukrainian staff that the site's fourth and last operational 750-Kilovolt power line was down after three others were lost earlier, it said in a statement on its website.

But IAEA experts also learned that a reserve line linking the facility to a nearby thermal power plant was delivering electricity to the external grid. This reserve line can also provide backup power to the plant if needed, it said.

The IAEA also said only one of the Zaporizhzhia plant's six reactors remained in operation.

IAEA Director-General Rafael Grossi said on Friday that six members of the agency's expert mission remained at the Zaporizhzhia plant, including four who will leave next week and another two who will stay there as the agency's continued presence in the longer term.

According to the IAEA, the experts will "carry out detailed and continuous work to assess the physical damage to the plant's facilities, determine the functionality of the main and backup safety and security systems and evaluate the staff's working conditions, in addition to performing urgent safeguards activities on the site."

The Zaporizhzhia plant, one of Europe's largest nuclear power plants, has been controlled by Russian forces since early March, but its Ukrainian staff has continued to operate it. Ukraine and Russia have traded accusations over recent strikes on the facility.

(With input from agencies)