The UN nuclear watchdog has said that the protective structure surrounding the exploded reactor at Chernobyl can no longer perform its main function of blocking radiation, after a Russian drone strike earlier this year.

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.