Ukraine and Russia have accused each other of planning a provocation at the site, raising alarm over risks of a radioactive disaster at Europe's largest nuclear plant.

"With military tension and activities increasing in the region where this major nuclear power plant is located, our experts must be able to verify the facts on the ground," IAEA head Rafael Grossi said in a statement.

The IAEA experts' "independent and objective reporting would help clarify the current situation... which is crucial at a time like this with unconfirmed allegations and counter allegations", he said.

In recent weeks, IAEA staff on site have inspected various locations, but so far have not observed "any visible indications of mines or explosives".

But the UN nuclear watchdog says it has been unable to access the rooftops of reactor units 3 and 4, as well as parts of the turbine halls and cooling system at the plant.

On Tuesday, Kyiv accused Moscow of planning "dangerous provocations" at the site, while Russia has accused Ukraine of similar plans.

The Ukrainian military claimed that "external objects similar to explosive devices were placed on the outer roof of the third and fourth reactors" at the site.

Russia and Ukraine have regularly accused each other of putting the plant's safety at risk since the Kremlin launched large-scale hostilities in Ukraine last February.