The International Atomic Energy Agency (IAEA) has repeatedly warned of the dangers of fighting around nuclear plants following Russia's full-scale military offensive into Ukraine in February 2022.

In the first days of the conflict, Russian forces seized the Zaporizhzhia nuclear plant in southern Ukraine, and also briefly held the decommissioned Chernobyl plant in the north.

Ukraine launched its surprise incursion into Kursk on August 6. It has said it is making advances, even as Russian forces move deeper into eastern Ukraine.

Russian President Vladimir Putin last week accused Ukraine of trying to attack the Kursk nuclear power plant, which is less than 50 kilometres (30 miles) from fighting between Russian and Ukrainian forces.

The IAEA confirmed that it had been told by Russian authorities that drone fragments were found last Thursday roughly 100 metres from the Kursk plant's spent fuel nuclear storage facility.

- 'Serious situation' -

Grossi said he would "independently assess what is happening" when he visits the plant on Tuesday, personally leading the mission "given the serious situation".

"The safety and security of all nuclear power plants is of central and fundamental concern to the IAEA," Grossi said in a statement on Monday.

The plant lies some 60 kilometres (37 miles) from the Russia-Ukraine border, next to the Seym river, and less than 50 kilometres away from Kursk city, the region's capital with a population of around 440,000.

The plant has four reactor units though only two are operational. Two more reactors are under construction.

All four reactors are the same type as Ukraine's Chernobyl nuclear power plant, without a protecting dome around them.

In 1986, a reactor at Chernobyl exploded during a botched safety test, resulting in the world's worst nuclear accident that sent clouds of radiation across much of Europe and forced tens of thousands of people to evacuate.

Tariq Rauf, a former IAEA official, said these types of reactors have since undergone "significant safety upgrades".

Robert Kelley, a former IAEA director of inspections, said: "The possibility of a Chernobyl-type incident with the reactor blowing up and burning for days is zero."

But he added that an errant bomb or large artillery strike on spent fuel storage ponds could damage the fuel and release radioactive gases and particles.

- 'Maximum restraint' -

Russia has repeatedly sounded the alarm over a possible hit since Ukrainian troops and tanks stormed into Kursk.

The IAEA urged both Russia and Ukraine to exercise "maximum restraint" to "avoid a nuclear accident with the potential for serious radiological consequences".

On Sunday, Ukraine's President Volodymyr Zelensky said Ukrainian forces had taken control of two more Russian settlements in Kursk region, adding to dozens already captured.

More than 130,000 people have been displaced so far.

Kyiv has said the offensive aims to prevent cross-border strikes from Russia into its Sumy region and to force Russia to the negotiating table "on our own terms".