Соответствующая норма
Practice Relating to Rule 117. Accounting for Missing Persons
Section A. Search for missing persons
Ukraine’s IHL Manual (2004) states:
“Missing persons” mean persons who are missing during hostilities and whose whereabouts are unknown.
Regarding such persons … as soon as circumstances permit (at the latest from the end of active hostilities) each Party to the conflict shall search for the persons who have been reported missing by an adverse Party. 
Ukraine, Manual on the Application of IHL Rules, Ministry of Defence, 11 September 2004, § 1.2.29.