Kyiv and Moscow have accused each other of planning "provocations" at the Zaporizhzhia nuclear plant in southern Ukraine, raising alarm over risks of a radioactive disaster.

The International Atomic Energy Agency (IAEA) on Wednesday called for additional access to the plant to "confirm the absence of mines or explosives at the site".

"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 the cooling system at the plant.

Fears over the safety of the nuclear plant have persisted throughout Russia's invasion.

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

On Wednesday, Ukraine called on the international community to respond to what it said was Russia's military escalation at the Zaporizhzhia plant.

- 'Time for immediate action' -

"It's high time the world took immediate action," the foreign ministry in Kyiv said.

"Russia deploying military personnel, installing fortifications on at least three reactors, placing explosives at the Zaporizhzhia nuclear power plant directly threatens a nuclear incident at Europe's largest atomic power station," the ministry said in a statement.

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.

In Russia, authorities claimed Kyiv was plotting an act of "sabotage."

"The situation is quite tense because the threat of sabotage from the Kyiv regime is really high -- sabotage that could have catastrophic consequences," Kremlin spokesman Dmitry Peskov told reporters on Wednesday.

The comments come after Ukrainian President Volodymyr Zelensky this week told his French counterpart Emmanuel Macron that Russia was planning "dangerous provocations" at plant, the largest in Europe.

"The Kyiv regime has repeatedly demonstrated its readiness not to rule anything out. Most recently, we saw this during the explosion of the Kakhovskaya hydroelectric power station, also with horrific consequences," Peskov said.

Russia and Ukraine have regularly accused each other of putting the plant's safety at risk since Russian President Vladimir Putin sent troops to Ukraine in February last year.