Related Rule
United Kingdom of Great Britain and Northern Ireland
Practice Relating to Rule 115. Disposal of the Dead
Section E. Grouping of graves according to nationality
The UK LOAC Manual (2004) states: “Graves must be respected and properly maintained. They must be marked so that they may always be found and should, if possible, be grouped according to the nationality of the deceased.” 
United Kingdom, The Manual of the Law of Armed Conflict, Ministry of Defence, 1 July 2004, § 7.36.