It will be unsafe to restart the Russian-held Zaporizhzhia nuclear power plant in Ukraine as long as war rages around it despite Moscow's hopes to fire up the complex, U.N. nuclear watchdog chief Rafael Grossi said on Monday.

Grossi held a meeting with Russia on the issue last week after officials including President Vladimir Putin told him Moscow hopes to restart Europe's biggest nuclear power plant, where the six reactors are now shut down as the International Atomic Energy Agency has recommended on safety grounds.

"The idea, of course, they have is to restart at some point. They are not planning to decommission this nuclear power plant. So this is what prompts the need to have a discussion about that," Grossi told a news conference on the first day of a quarterly meeting of the IAEA's 35-nation Board of Governors.

Russia said after last week's meeting it is not currently planning to reactivate the plant. Grossi said some important steps need to be taken before it can restart safely.

"In terms of what needs to happen ..., there shouldn't be any bombing or any activity of this type," Grossi said.

"Then there should be a more stable assurance of external power supply. This requires repairs, important repairs of existing lines, which at the moment, and because of the military activity, are very difficult to envisage."

Russia and Ukraine have blamed each other for periodic shelling that has downed the plant's power lines. Last month the plant was attacked by drones that hit a reactor building in the worst such incident since November 2022, though nuclear safety was not compromised, the IAEA said at the time.

"The attacks and the frequent disconnection of the off-site power lines due to military activity are creating a grave situation," Grossi said in a statement to the Vienna-based IAEA Board earlier on Monday.

External power is essential to prevent a potentially catastrophic meltdown at a nuclear power plant like Zaporizhzhia since it is needed to cool fuel in the reactors even when those reactors are shut down.

Zaporizhzhia is currently reliant on one of its four main power lines and a backup line for external power. Since Russia seized the plant weeks after it invaded Ukraine in February 2022, the plant has lost all external power eight times, forcing it to rely on emergency diesel generators for power.

(Reporting by Francois Murphy; editing by Mark Heinrich)