British defense officials are warning of the possibility of more flooding over the next few days following a dam breach in southern Ukraine. Observers say the impact of the incident on Ukraine's counteroffensive against Russia should be limited.

Ukraine's military announced on Tuesday that the dam at the Kakhovka hydroelectric power plant on the Dnipro River in the Kherson region was destroyed by Russians.

A local governor said efforts were underway to evacuate the roughly 16,000 residents exposed to the danger of flooding.

Ukrainian President Volodymyr Zelenskyy said on social media on Wednesday that at least tens of thousands of people remain in the area even after the start of Russia's invasion. He also said hundreds of thousands of people have been left without normal access to drinking water.

Russian officials in the area told the state-run TASS news agency that seven people were reported missing in areas controlled by Moscow.

Ukraine blames Russia for carrying out an internal detonation of the dam's structures.

Russia says Ukraine sabotaged the dam.

The British defense ministry tweeted on Wednesday that the water level in the dam was at a record high before the collapse. It said this resulted in a particularly high volume of water inundating the area downstream.

The ministry also said the Zaporizhzhia nuclear power plant, whose cooling water is supplied from the dam, is highly unlikely to face immediate additional safety issues as a result of the dropping water levels in the reservoir.

But it said the dam's structure is likely to deteriorate further over the next few days, causing more flooding.

The US think tank Institute for the Study of War said it had not yet observed clear evidence of what happened at the Kakhovka plant on Tuesday and was unable to offer an independent assessment of responsibility.

The institute also said Ukrainian officials offered assurances that the damage to the dam and subsequent flooding would not impede Ukrainian counteroffensive preparations.

It said the areas impacted by the flooding are very far from the frontline and that the flooding is not likely to affect the areas that have seen active fighting recently.

Russia's defense ministry says Ukrainian forces have begun their counteroffensive.

British defense officials also say there has been a substantial increase in fighting along numerous sectors of the frontline, suggesting that moves by Ukraine's military to retake its territory are entering a new phase.