A former high-ranking British army officer has slammed Russian strongman Vladimir Putin as a “lunatic” and “terrorist” — claiming that he essentially turned a Ukrainian power plant into a makeshift nuclear bomb after his forces blew up a large dam Tuesday.

Hamish de Bretton-Gordon, a chemical weapons expert and former colonel, made the comments to The Sun after Russian troops blew up the massive Kakhovka dam in southern Ukraine.

Floodwaters were expected to reach “critical levels” in a matter of hours, according to Oleksandr Prokudin, the head of the Kherson Regional Military Administration.

The hydroelectric dam, which holds about 4.8 billion gallons of water, provides cooling water to the Russian-controlled Zaporizhzhia plant, Europe’s largest nuclear power facility.

Russian officials said there was no immediate danger to the nuke plant due to the dam explosion — but Bretton-Gordon had harsh words for the Kremlin leader.

He warned about catastrophic consequences if the dam’s explosion interferes with the plant’s critical water or power supplies – and accused Moscow of essentially turning the facility into an “improvised nuclear device” due to Russian recklessness.

Officials with the International Atomic Energy Agency said they are monitoring the situation, adding that there was no “immediate risk,” according to The Sun.

Aerial footage shared by Ukrainian President Volodymyr Zelensky shows gushing water overtaking the dam and spilling into the river below.

The plant, which is staffed by a skeleton crew, has six reactors – five in cold shutdown and one in hot shutdown, according to the UK news outlet.

But Bretton-Gordon warned that the reactors could still go critical if they can’t get enough water or power to keep them cool.

He told The Sun that the Russians exhibited escalation and desperation by blowing up the dam and he called for immediate international efforts to secure the nuke plant.

“There is a lot of nuclear fuel in the reactors and it needs a lot of water and power to keep it cool,” the former colonel told The Sun. “It is absolutely careless, a terrorist act by a terrorist state, it’s almost unbelievable.”

Bretton-Gordon warned of “another Chernobyl” – the catastrophic 1986 nuclear disaster in Soviet-controlled Ukraine — should ancient generators be relied on to run the plant in case of power outages caused by flooding.

“Even though it’s a well-built modern power station, this would not have been considered. It’s almost too ridiculous,” he said. “But now you’ve got a lunatic like Putin running things who is prepared to do anything, it’s very challenging.”

Bretton-Gordon called for a demilitarized zone around the Zaporizhzhia plant to avert a possible nuclear disaster.  

“Ultimately this is another nail in Putin’s coffin and we have to keep our fingers crossed the plant doesn’t go bang,” he told The Sun.

“Everything must be done to make sure that doesn’t happen,” the expert said.

Bretton-Gordon also said Russian forces will use the flooding to slow the Ukrainian counter-offensive by “creating an obstacle.’

“This is a desperate roll of the dice, it’s one short of going nuclear or using chemical weapons,” he told the outlet. “The Russians realize what the Ukrainians have with their attacking force is very potent, and they are doing all they can to stop them.

“This is a terrible crime, another war crime to add to Putin’s charge sheet, but I’m sure the high command in Kyiv would have war-gamed this situation,” he said.

Prokudin, the head of the Kherson Regional Military Administration, also labeled the Russians as “terrorists.”

“The destruction of the Kakhovka hydroelectric power plant dam only confirms for the whole world that they must be expelled from every corner of Ukrainian land,” he wrote on Twitter.

“Not a single meter should be left to them, because they use every meter for terror. It’s only Ukraine’s victory that will return security. And this victory will come. The terrorists will not be able to stop Ukraine with water, missiles or anything else,” he added.

Zelensky has called an emergency meeting to plan a response to the dam explosion.