Work already has started into an investigation by the International Criminal Court of the breach of the Kakhovka dam and the vast flood it triggered, Ukrainian President Volodymyr Zelenskyy said on Sunday.

"Representatives of the International Criminal Court have visited Kherson region in recent days," Zelenskyy said in his nightly video address.

"On the very first day after the disaster, the general prosecutor's office sent a corresponding request to the International Criminal Court concerning an investigation of this disaster, and the work has already begun."

Zelenskyy said it was important that international legal experts saw the aftermath of the disaster, including incidents of shelling of flooded areas. Officials said three people were killed on Sunday in Russian shelling of boats carrying evacuees.

The president said Ukrainian rescue teams had evacuated about 4,000 residents from affected zones — including areas on the Russian-occupied east bank of the Dnipro River.