Originally Posted by
etudiant
The UN data is what seems most solid for civilian deaths
Yes, but that's just what they can confirm with certainty. They don't have access to places like Mariupol to check each recently burried person and determine the cause of death and if they were military or civilian. For that reason, every UN report mentions that they believe the real figures are considerably higher:
OHCHR believes that the actual figures are considerably higher, as the receipt of information from some locations where intense hostilities have been going on has been delayed and many reports are still pending corroboration. This concerns, for example, Mariupol (Donetsk region), Izium (Kharkiv region), Popasna, Lysychansk, and Sievierodonetsk (Luhansk region), where there are allegations of numerous civilian casualties.