Ukraine has informed the International Atomic Energy Agency that staff who have been kept at the Chernobyl nuclear power plant since Russian troops took control of the site a week ago are facing “psychological pressure and moral exhaustion”, the United Nations’ atomic watchdog has said.

IAEA director general Rafael Mariano Grossi said that the staff must be allowed to rest and rotate so their crucial work can be carried out safely and securely.

Mr Grossi received “a joint appeal from the Ukraine Government, regulatory authority and the national operator which added that personnel at the Chernobyl site ‘have limited opportunities to communicate, move and carry out full-fledged maintenance and repair work’,” the IAEA said in a statement.

Reactor number four at the power plant exploded and caught fire in 1986, shattering the building and spewing radioactive material high into the sky.

Even 36 years later, radioactivity is still leaking from history’s worst nuclear disaster.

Ukraine has lost regulatory control over all the facilities in the Chernobyl exclusion zone to the Russians and asked the IAEA to undertake measures “in order to reestablish legal regulation of safety of nuclear facilities and installations” within the site, the statement added.

Mr Grossi has repeatedly stressed that any military or other action that could threaten the safety or security of Ukraine’s nuclear power plants must be avoided.

“I remain gravely concerned about the deteriorating situation in Ukraine, especially about the country’s nuclear power plants, which must be able to continue operating without any safety or security threats,” he said.

“Any accident caused as a result of the military conflict could have extremely serious consequences for people and the environment, in Ukraine and beyond.”