Kyiv has accused Russia of repeatedly targeting the facility, the site of a 1986 meltdown that is still the world's worst ever nuclear disaster, since Moscow invaded in February 2022.

A hit earlier this year punched a hole in the outer radiation shell, triggering a warning from the International Atomic Energy Agency (IAEA) that it had "lost its primary safety functions."

In an interview with AFP, plant director Sergiy Tarakanov said fully restoring that shelter could take three to four years, and warned that another Russian hit could see the inner shell collapse.

"If a missile or drone hits it directly, or even falls somewhere nearby, for example, an Iskander, God forbid, it will cause a mini-earthquake in the area," Tarakanov told AFP in an interview conducted last week.

The Iskander is Russia's short-range ballistic missile system that can carry a variety of conventional warheads, including those to destroy bunkers.

"No one can guarantee that the shelter facility will remain standing after that. That is the main threat," he added.

The remnants of the nuclear power plant are covered by an inner steel-and-concrete radiation shell -- known as the Sarcophagus and built hastily after the disaster -- and a modern, high-tech outer shell, called the New Safe Confinement (NSC) structure.

The roof of the NSC was severely damaged in a Russian drone strike in February, which caused a major fire in the outer cladding of the steel structure.

"Our NSC has lost several of its main functions. And we understand that it will take us at least three or four years to restore these functions," Tarakanov added.

The IAEA said earlier this month an inspection mission found the shelter had "lost its primary safety functions, including the confinement capability, but also found that there was no permanent damage to its load-bearing structures or monitoring systems."

Director Tarakanov told AFP that radiation levels at the site remained "stable and within normal limits."

The hole caused by the drone hit has been covered with a protective screen, he said, but 300 smaller holes made by firefighters when battling the blaze still need to be filled in.

Russia's army captured the plant at the start of its 2022 invasion, before withdrawing a few weeks later.