Kyiv: Andriy Yermak, the head of the president's office, reported on Wednesday that a Russian drone attack in the northern Ukrainian region of Sumy resulted in the deaths of two civilians and the injury of a third.

A "Shahed" drone made in Iran destroyed and set fire to a private residence, according to Yermak on the Telegram messaging app. Russia repeatedly shelled the northeastern border region during the night and on Wednesday morning, according to a statement from the president's office.

A large Russian-held dam in southern Ukraine came under attack, causing a torrent of water to be released that inundated two dozen villages, flooded a small city, and forced 17,000 people to flee.

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The environmental and humanitarian effects of the attack, for which Moscow and Kiev traded blame, were likely to be much more significant, the UN cautioned.

"We are gravely concerned about the destruction of the Kakhovka Dam,... and the severe humanitarian impact on hundreds of thousands of people on both sides of the front line," the UN agency for humanitarian affairs OCHA stated.

The agency noted that "thousands have lost their homes overnight," and that "thousands more have lost access to water, food, and basic services," citing reports from Ukrainian authorities that nearly 40 towns and villages were fully or partially flooded.

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OCHA warned that while the extent and effects of the dam's destruction and the Kakhovka Reservoir's reduction were still being assessed, they were "projected to have severe and longer-term consequences on the humanitarian situation in the area."

The document issued a warning that, among other things, "flooding and fast-moving water can move mines and explosive ordnance to new areas which previously had been assessed as safe, thus putting more people in danger."

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OCHA reported that urgent humanitarian assistance, including water supplies, was being provided to more than 16,000 people.