The United Nations says Russia has been denying aid workers access to Russian-controlled areas flooded by the breach of a dam in southern Ukraine.

A senior UN relief official said in a statement on Sunday that Russia has so far declined requests to reach residents of Russian-controlled areas of southern Ukraine impacted by the breach of the Kakhovka dam.

The official said that the UN urges Russian authorities to act in accordance with their obligations under international humanitarian law. She stressed, "Aid cannot be denied to people who need it."

The UN's Deputy Spokesperson for the Secretary-General, Farhan Haq, told reporters on Monday that the UN will continue to do all it can to reach people who need aid, no matter where they are.

On the same day, Russia's presidential spokesperson Dmitry Peskov blamed Ukraine's military for hampering UN relief work. He said that there has been constant shelling and constant provocations, so that it's very hard to ensure the security of aid workers.

A leader of pro-Russian forces in the southern Ukrainian region of Kherson said on Sunday that the dam's breach has left 35 people dead in the Russian-controlled areas.

Ukraine's internal affairs ministry said on Monday that 18 civilians have been confirmed dead and 31 others remain unaccounted for since the dam collapsed.

The ministry stressed that it continues relief efforts amid Russian shelling.