The United Nations said on Sunday that Moscow had declined requests to help residents of Russian-controlled areas of southern Ukraine affected by the breach of the Kakhkova dam and vowed to press on with humanitarian efforts.
The bursting of the dam on a hydroelectric station has flooded vast areas and created difficult conditions for thousands made homeless or without vital services.
Ukrainian Interior Minister Ihor Klymenko, writing on Facebook, put at 17 the death toll from the dam's destruction, with 31 still missing. He said nearly 900 homes remained under water and more than 3,600 people had been evacuated.
The UN statement, issued by its humanitarian coordinator for Ukraine, Denise Brown, said the world body "will continue to engage to seek the necessary access."
"We urge the Russian authorities to act in accordance with their obligations under international humanitarian law. Aid cannot be denied to people who need it."
Ukraine and Russia blame each other for the breach
Parts of Ukraine's Kherson region, seized by Russian troops in the first days of the February 2022 invasion, remain under Russian control.
Ukrainian officials have repeatedly accused Russia of failing to evacuate or provide for the elementary needs of those in Moscow-controlled areas.
Kyiv reported at least one incident of Russian shelling of residents being evacuated in which three people were killed.
Andrei Alekseyenko, chairman of the Russian-installed administration in the Moscow-occupied parts of Kherson region, said on the Telegram messaging app the death toll had risen to 29 people.
A team of international legal experts assisting Ukraine's prosecutors in their investigation said in preliminary findings on Friday it was "highly likely" the destruction of the dam was caused by explosives planted by Russians.
The Kremlin accuses Kyiv of sabotaging the hydroelectric dam, which held a reservoir the size of the US Great Salt Lake, to cut off a key source of water for Crimea and distract attention from a "faltering" counter-offensive against Russian forces.