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.

Earlier this week, Grossi said the watchdog had requested access to the rooftops of two reactor units, as well as parts of the turbine halls and cooling systems.

"I think we are making progress," he said Friday in Tokyo.

"We have been able to complete the tours of the cooling ponds and other places," he said, adding they had "not seen any indications of explosives or mines."

He said IAEA officials had not yet been able to visit the facility's rooftops.

"I'm pretty confident that we will get this authorisation," he added.

"This is a combat zone, it's an active warzone, so sometimes it may take a day or two to get the authorisations."

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.

Fears over the plant have persisted throughout Moscow's Ukraine offensive and been exacerbated by the destruction of a dam that provided the cooling water for the plant.

Grossi said the IAEA had contingency plans for various scenarios at the plant and "we do have a clear assessment of what emergency preparedness and response mechanisms should be in place should something occur."