Russia has formed special groups to collect and hide bodies of people killed in the aftermath of the breach this month of the Kakhovka dam in southern Ukraine, President Volodymyr Zelenskiy said on Thursday.

"The Russian evil has formed special groups there to remove and, obviously, hide the victims' bodies," Zelenskiy said in his nightly video address.

Zelenskiy described the situation in Russian-occupied parts of the region as "catastrophic to put it mildly".

Ukraine and Russia have accused each other of being behind the breach.

The dam's destruction sent high waters cascading through parts of southern Ukraine downriver from the dam, particularly the Kherson region, partly occupied by Russian troops.

Many people were forced onto rooftops to await rescue and Ukraine accused Russian occupying forces of inaction in helping those affected. Residents have lacked sanitation and drinking water.

Ukrainian officials have put the official death toll at 21, including five people who died from what they described as Russian shelling during evacuation operations. Russian officials have put the death toll at 46.

The Ukrainian military said on Thursday that the epidemiological situation in affected areas had worsened sharply, especially as regards the spread of hepatitis A.

Ukrainian Environment Minister Ruslan Strilets has estimated at more than $1.5 billion the cost so far of the damage caused by the catastrophe.