Règle correspondante
Sweden
Practice Relating to Rule 20. Advance Warning
Sweden’s IHL Manual (1991) states: “Should it be impossible to suspend or cancel the attack, excessive losses among the civilian population may possibly be avoided by giving the civilian population advance warning.” 
Sweden, International Humanitarian Law in Armed Conflict, with reference to the Swedish Total Defence System, Swedish Ministry of Defence, January 1991, Section 3.2.1.5, p. 72.