Chernobyl has stopped sending safety signals to nuclear authorities after the plant was taken over by Russia in its invasion of Ukraine.
Officials said it was also “increasingly urgent and important” to rotate staff who had been working since forces took control around two weeks ago.
The International Atomic Energy Agency (IAEA) provided an update on the situation at Chernobyl on Tuesday night, saying safeguard monitoring systems - which monitor nuclear material - had stopped sending data to the United Nations watchdog.
The organisation - which aims to prevent the use of nuclear energy for military purposes - said it was looking into the safety monitoring systems at other locations in Ukraine.
Russian troops seized a radioactive waste facility near the defunct power plant where the world’s worst nuclear accident happened in 1986 in the first days of its invasion launched in late February.
They have also targeted Zaporizhzhia, Europe’s largest nuclear power plant, and fired rockets at a physics institute containing a nuclear reactor in Kharkiv.
An energy expert warned on Tuesday Russia could be attacking and taking over key nuclear sites to give it leverage to blackmail the international community.
Dr Aura Sabadus from Independent Chemical and Energy Market Intelligence, an energy data firm, said another reason could be Russia was trying to “create some kind of havoc” by targeting power plants ensuring a steady stream of electricity supply.
Authorities have raised concerns over staff who had been on duty at the Chernobyl plant since it was taken over on 24 February, which were renewed by the IAEA in its statement on Tuesday.
Rafael Mariano Grossi, the IAEA director general, said: “I’m deeply concerned about the difficult and stressful situation facing staff at the Chornobyl nuclear power plant and the potential risks this entails for nuclear safety.
He added: “I call on the forces in effective control of the site to urgently facilitate the safe rotation of personnel there.”
The regulator said the same workforce had been “in effect living there” for the past 13 days and while they had access to food, water and medicine, conditions were “worsening”.
The IAEA said staff at nuclear facilities must be able to rest and work in regular shifts, as this was “crucial for overall nuclear safety”.
