II. What is a ‘siege’ and is it prohibited?
IHL treaties refer to ‘besieged’ or ‘encircled’ areas but do not define them.6 Nor are sieges defined in other areas of public international law. Unlike occupation or naval blockades, there are no specific conditions that must be met for a siege to be established and for specific rules to become applicable.
The essence of siege operations is the isolation of besieged enemy forces in terms of their separation from reinforcements and logistical supplies.7 There is no need for total encirclement. What matters is the effect of the positioning of the besieging forces. They must be in a position to control entry and egress from a particular area, and thus movement in and out of weapons and ammunition, supplies and people.8
Sieges typically combine two key constituent elements: ‘encirclement’ of an area for the purpose of isolating it, and bombardment. Encirclement is the defining characteristic of sieges. It is usually accompanied by bombardment – the frequency and intensity of which will vary. If the purpose of the siege is to contain enemy forces, there may be no need for bombardment, unless the forces attempt to flee. The situation is different if the objective of the siege is either to force the enemy to surrender or to assume control of the besieged area.
Concerns about the compatibility of sieges with modern rules of IHL arise because attacks into besieged areas and the isolation of the besieged forces will also adversely impact any civilians in the besieged areas; civilians are likely to be affected sooner and to a greater extent than the fighters against whom the isolation is directed.
Sieges are not prohibited as such under either IHL or other areas of public international law. Under IHL, the besieging party is entitled to attack forces and other military objectives in besieged areas, and to limit supplies that reach them. However, in doing so it must comply with all relevant rules of IHL: the few that specifically refer to sieges, as well as the generally applicable rules that regulate the conduct of hostilities and afford civilians protections and safeguards.
6 Article 27 Regulations concerning the Laws and Customs of War on Land annexed to 1907 Convention (IV) respecting the Laws and Customs of War on Land (1907 Hague Regulations); Article 15 1949 Geneva Convention for the Amelioration of the Condition of the Wounded and Sick in Armed Forces in the Field (GC I); Article 18 1949 Geneva Convention For the Amelioration of the Condition of Wounded, Sick and Shipwrecked Members of Armed Forces at Sea (GC II); and Article 17 1949 Geneva Convention relative to the Protection of Civilian Persons in Time of War (GC IV).
7 See, for example, United States Department of the Army (2006), Field Manual 3-06, Urban Operations, III-19: ‘[p]hysical isolation involves interdicting the movement of units, persons, weapons, supplies, funds, contraband and other shipments into the urban area.’
8 For example, ibid., III-18: ‘[i]solation involves identifying and controlling the most important ingress points into the urban area (and adapting as the adversary finds different routes). The level of granularity required in isolating an urban area will depend on the nature of the threat.’ See also Hampson, F. (2015), ‘Can Siege Warfare Still be Legal?’, in College of Europe (2015), ‘Proceedings of the Bruges Colloquium, Urban Warfare’, 16th Bruges Colloquium, p. 89 at p. 91.