Ukraine accuses Russia of turning the plant into a shield for its artillery guns and dynamiting the reactor roof, turning the site into an atomic bargaining chip.

International Atomic Energy Agency experts are "still awaiting access to the rooftops of the reactor buildings," IAEA Director General Rafael Grossi said in a statement.

Kyiv and Moscow have accused each other of planning an incident at the plant, which fell to Russian forces at the start of their invasion launched in February last year.

Kyiv has said Russia has placed explosives on the plant and President Volodymyr Zelensky has urged the international community to intervene.

Faced with these mutual accusations, the IAEA had demanded better access in order to "verify the facts on the ground", in an "independent and objective" way.

Grossi later reported progress as his team was able to visit the fuel cooling pools. But a request to inspect the roofs has now been pending for nearly two weeks.

The IAEA said that so far it had not detected any "visible indication of explosives or mines", adding that there was a "volatile security situation in the region located on the frontline of the conflict".

After falling into Russian hands, Europe's biggest power plant was targeted by gunfire and has been severed from the grid several times, raising fears of a major nuclear accident.