Inspectors from the International Atomic Energy Agency (IAEA) began a rare visit to Ukraine on December 1, to assess the status of key electrical substations supplying the country's three nuclear sites that are still operational.

As part of the trip, the team also checked the defunct Chernobyl site's New Safe Confinement (NSC), which was put in place to stop the release of radioactive material after the explosion of one of its reactors in 1986.

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

"The mission confirmed that the NSC 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," the IAEA said in a statement on Friday.

IAEA director general Rafael Grossi added: "Limited temporary repairs have been carried out on the roof but timely and comprehensive restoration remains essential to prevent further degradation and ensure long-term nuclear safety."

The NSC was installed in 2016 and officially inaugurated in 2019, replacing an original "sarcophagus" built by the Soviets.

The IAEA said further temporary repairs to re-establish the confinement function would take place in 2026, "paving the way for full restoration once the conflict ends" between Ukraine and Russia.