This marked the seventh time that Europe’s largest nuclear power plant had been completely disconnected from the national electricity grid since the start of the full-scale Russian invasion 15 months ago, the agency said, noting that the facility was forced to run on emergency diesel generators once again.

The plant’s only remaining external 750 kilovolt power line had been cut around 5:30am, local time, and re-connected after more than five hours, according to IAEA experts located at the facility.

‘We’re playing with fire’

Agency chief Rafael Mariano Grossi said the situation demonstrated “the highly vulnerable nuclear safety and security situation” at the plant, which has come under shelling during the conflict.

“As I’ve said repeatedly, this simply can’t go on. We’re playing with fire. We must act now to avoid the very real danger of a nuclear accident in Europe, with its associated consequences for the public and the environment.”

The ZNPP was occupied by Russian forces in the early days of the war and is still being operated by Ukrainian personnel.

Most staff live in the nearby town of Enerhodar. On Friday, the IAEA reported that a location close to the town came under artillery fire earlier that day.

Intense negotiations continue

Mr. Grossi said he continues to engage in intense negotiations with all parties to secure the protection of the nuclear plant, stressing that “I will not stop until this has been achieved.”

He explained that the ZNPP does not have any operational back-up power lines since the last one functioning had been damaged in March, which has still not been repaired.

“For more than two and a half months, this major nuclear power plant has only had one functioning external power line. This is an unprecedented and uniquely risky situation. Defence-in-depth – which is fundamental to nuclear safety – has been severely undermined at the ZNPP,” he said.

Still awaiting access

He called for greater efforts to restore the back-up power lines, while also reiterating the need for the IAEA team on site to gain access to the Zaporizhzhya Thermal Power Plant (ZTPP), located nearby.

The ZTPP has an open switchyard through which back-up power has been provided to the nuclear plant in the past. Access has yet to be granted despite reassurances by the Russian state nuclear company, Rosatom.

Following the off-site power cut on Monday, all the nuclear plant's 20 diesel generators started operating. However, 12 were later switched off, leaving eight running, which is sufficient to operate all systems safely.

The IAEA said its experts at the site were informed that there is enough diesel fuel for 23 days, adding that after the 750 kilovolt line was restored, the diesel generators were gradually turned off.