Moscow and Kyiv have blamed each other for the damage at the Kakhovka hydroelectric dam, which has led to thousands of people being evacuated because of flooding.

The Kakhovka dam sits on the Dnipro river, which feeds a reservoir providing cooling water for the Russian-occupied Zaporizhzhia nuclear power station, some 150 kilometres (90 miles) away.

- 'No immediate risk' -

The International Atomic Energy Agency (IAEA) -- which has a team of experts at the plant -- said it was "closely monitoring the situation" at the plant but saw "no immediate nuclear safety risk".

Karine Herviou, the deputy head of France's IRSN nuclear safety regulator, also told AFP there was "no immediate risk to the safety of the plant".

"There is no risk of flooding of the plant since the dam is downstream, not upstream," she added.

The plant's Russian-installed director, Yuri Chernichuk, insisted there was no security threat to the plant.

But Ukraine -- which in 1986 suffered the devastating Chernobyl nuclear disaster -- sounded the alarm.

Ukrainian presidential aide Mykhaylo Podolyak said the world "once again finds itself on the brink of a nuclear disaster".

- Depleting reservoir -

Damage to the dam was leading to a reduction in the height of the reservoir of about five centimetres (two inches) per hour, IAEA head Rafael Grossi said in a statement to his agency's 35-member board of governors.

Water in the reservoir was at around 16.4 metres early Tuesday, and if it drops below 12.7 metres, then it can no longer be pumped to the plant, Grossi warned, adding this could happen in "a few days".

Plant staff were making "all efforts to pump as much water into its cooling channels and related systems as possible", while supplies for "non-essential consumers of water" at the plant were being stopped, he added.

Besides that, IAEA is looking to confirm whether a large cooling pond next to the site would be able to provide water for cooling "for some months", he said, adding that this pond "by design is kept above the height of the reservoir".

"It is therefore vital that this cooling pond remains intact. Nothing must be done to potentially undermine its integrity. I call on all sides to ensure nothing is done to undermine that," said Grossi, adding he will visit the plant next week.

Herviou said the damaged dam was "worsening" the situation at the plant, but "in any case, we have time, probably a few weeks" to look for solutions.

One option could be to bring truck water to the site "even if this is not necessarily easy in times of war".

- Shut-down reactors -

The plant's reactors have already been shut down, but they still need cooling water to ensure there is no nuclear disaster.

"Absence of cooling water in the essential cooling water systems for an extended period of time would cause fuel melt and inoperability of the emergency diesel generators," Grossi warned.

Herviou also said the fact that the reactors have been shut down for several months -- the last one in September -- was "good news".

"The impact is therefore lower," she added.

Grossi has repeatedly called for the protection of the plant as shelling has taken place near it and also several times disrupted its crucial power supply.

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