A Russian drone attack has hit the radiation shelter over the damaged reactor at the Chernobyl nuclear power plant, Ukrainian President Volodymyr Zelensky has said.

The overnight strike hit the shelter of the destroyed former fourth power unit at the plant, causing a fire that has since been extinguished, he added.

As of Friday morning, radiation levels had not increased at the plant, Zelensky said.

The International Atomic Energy Agency (IAEA) said fire safety personnel and vehicles responded within minutes of an overnight explosion. No casualties were reported, the agency added.