Related Rule
Practice Relating to Rule 8. Definition of Military Objectives
Section H. Areas of land
Sweden’s IHL Manual (1991) states:
The definition [of military objectives contained in Article 52(2) of the 1977 Additional Protocol I] is intended to apply only to property or objects. Thus, for example, areas of land cannot be included; but this does not prevent an area objective if it is a matter of hindering an enemy advance by means of artillery fire or mining. Attacks on an area are permitted as long as the attack cannot be classified as indiscriminate. 
Sweden, International Humanitarian Law in Armed Conflict, with reference to the Swedish Total Defence System, Swedish Ministry of Defence, January 1991, Section, p. 54.