Ukraine has four active nuclear power plants, providing about half the country's electricity, as well as stores of nuclear waste such as the one at Chernobyl, and fears linger over the possible consequences should they be damaged in the fighting.

Chernobyl was the site of the worst nuclear accident in history in 1986 and last Thursday the site fell to Russian troops.

"The best action to ensure the safety and security of Ukraine's nuclear facilities and its people would be for this armed conflict to end now," Director General Rafael Grossi told the International Atomic Energy Agency (IAEA) board of governors meeting.

"It is the first time a military conflict is happening amidst the facilities of a large, established nuclear power programme," he said.

A diplomatic source told AFP that a resolution had been drafted condemning Russia's invasion. Given the current composition of the board of governors, some form of resolution is likely to be approved by a majority of states.

While Grossi himself has avoided direct criticism of either party to the conflict, member states allied to Ukraine may push for tough wording towards Russia in the resolution.

The US delegation at the meeting had a Ukrainian flag affixed to their desk bearing the words: "Today we are all Ukraine".

On Monday, Grossi said he had received reports that Russian soldiers were close to the Zaporizhzhia station in eastern Ukraine.

Grossi has warned that any "accident involving the nuclear facilities in Ukraine could have severe consequences for public health and the environment".

On Wednesday, he said it was "imperative to ensure that the brave people who operate, regulate, inspect and assess the nuclear facilities in Ukraine can continue to do their indispensable jobs safely, unimpeded and without undue pressure".