Rishi Sunak said the destruction of the Kakhovka dam in Ukraine would mark a “new low” in the conflict if Russian forces were found to be responsible.
The Prime Minister said the immediate priority was the humanitarian response to the catastrophe, which has flooded villages, endangered vital crops and threatened drinking water supplies.
Mr Sunak, speaking to reporters as he travelled to Washington for talks with US President Joe Biden, said if it was an intentional act to blow up the dam it would be “the largest attack on civilian infrastructure” since the start of Vladimir Putin’s war.
He said that attacks on civilian infrastructure were “appalling and wrong”.
Kyiv accused Russian forces of blowing up the dam and hydroelectric power station in an area that Moscow has controlled for more than a year, while Russia blamed Ukrainian bombardment in the contested area.
Mr Sunak said: “Our military and intelligence agencies are currently looking at it, so it’s too soon to pre-empt that and make a definitive judgment.
“But what I can say is if it is intentional, it would represent, I think, the largest attack on civilian infrastructure in Ukraine since the start of the war, and just would demonstrate the new lows that we would have seen from Russian aggression.
“Attacks on civilian infrastructure are appalling and wrong. We’ve seen previous instances of that in this conflict so far, but it’s too early to say definitively.”
Asked whether the subject would be raised with the US President at their meeting on Thursday, Mr Sunak said: “Of course I’ll be discussing Ukraine with President Biden, generally, but the immediate response is humanitarian.
“So we had already put resources and funding in place to support both the UN and the Red Cross to respond to situations like this.
“And they are now being able to divert those resources to particularly help the humanitarian response and the evacuation in this area as a result of what’s happened.
“So we were already thinking ahead about situations like this, and I’m pleased that the UK is continuing to support Ukraine in lots of different ways.”
Officials have described the breach as an “ecological disaster”, while Ukrainian authorities have ordered hundreds of thousands of residents downriver to evacuate.
Foreign Secretary James Cleverly described it as an “abhorrent act”, adding that “intentionally attacking exclusively civilian infrastructure is a war crime”.
There are concerns that the damage to the dam could have broad consequences: flooded homes, streets and businesses downstream; depleted water levels upstream that help cool Europe’s largest nuclear power station; and drained supplies of drinking water to the south in Crimea, which Russia illegally annexed.
The deputy head of the Office of the President of Ukraine said the “ecocide” was “really terrible”.
Igor Zhovkva told BBC Radio 4’s World At One programme Russia’s claims that shelling had caused the damage were “absurd,” saying: “I know that there was a blast and it was made on purpose because you cannot ruin this dam (only) by shelling.”
But Evgeny Popov, a member of the Duma for Vladimir Putin’s United Russia party, claimed Ukraine would “profit” from the damage and said Russia is evacuating 22,000 people from the area.
He accused Ukraine of a “war crime” by carrying out the attack.
“We don’t need to do that. We are not attacking civilian infrastructure,” he told the same programme.
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