Chatham House briefing
Published 27 June 2019
Updated 14 December 2020
ISBN: 978 1 78413 333 7
Siege warfare has been employed throughout the ages and remains dramatically relevant today. Questions of the compatibility of this practice with international humanitarian law (IHL) arise when besieged areas contain civilians as well as enemy forces. This briefing addresses those rules of IHL that are particularly relevant to sieges.
Three sets of rules of IHL are of particular relevance to sieges. The first comprises the rules regulating the conduct of hostilities; these are primarily of relevance to the bombardment dimension of sieges. The second set is the prohibition of starvation of civilians as a method of warfare, as well as the rules regulating humanitarian relief operations; these are of relevance to the encirclement dimension. The third comprises the rules on evacuations, which can provide a way of alleviating the adverse effects of sieges on civilians. This briefing proceeds on the assumption that all these rules are the same in both international and non-international armed conflicts.
It is not just the besieging party that has obligations. The besieged party must also comply with a number of rules that play an important role in protecting civilians in besieged areas and in reducing the adverse impact of sieges on civilians.
For the purpose of applying these key rules of IHL, the bombardment and encirclement elements of sieges must be considered separately. A question that remains unsettled is whether, in addition, a siege as a whole must also comply with these rules.
The rules regulating the conduct of hostilities are primarily of relevance to the bombardment dimension of sieges. The discussion below focuses on bombardments, but any act that amounts to an ‘attack’ conducted in the context of a siege, such as sniping or other small arms fire, must also comply with these rules. The encirclement dimension of sieges is relevant to the application of these rules as they take into account the context in which the bombardment occurs.
To the extent that bombardment is used during a siege, it must comply with the relevant rules of IHL regulating the conduct of hostilities. Bombardments constitute an ‘attack’ as this term is defined in Additional Protocol I of 1977 to the Geneva Conventions of 1949 (AP I): ‘acts of violence against the adversary, whether in offence or in defence’.10 This means that bombardments must comply with a number of key rules: they must be directed exclusively against military objectives;11 they must not be indiscriminate;12 and they must comply with the rule of proportionality.13 Moreover, in the conduct of all military operations, belligerents must take constant care to spare the civilian population and civilian objects, and besieging and besieged forces must take a number of precautionary measures.14
The confined environment of a siege, where fighters and civilians find themselves in extremely close proximity, raises practical challenges for the application of the rules set out above. Many of these challenges also arise in other situations of urban warfare.
Besieging forces are entitled to direct attacks against enemy forces and other military objectives in besieged areas, provided of course that these attacks comply with other relevant rules
Besieging forces are entitled to direct attacks against enemy forces and other military objectives in besieged areas, provided of course that these attacks comply with other relevant rules. Article 27 of the 1907 Hague Regulations – the first of the four IHL treaty provisions that specifically refers to sieges – sets out a limited obligation to ‘spare’ certain civilian objects when conducting attacks.15 But it is uncontroversial that, following the extensive codification of the rules regulating the conduct of hostilities that has taken place since 1907, attacks directed against all civilian objects are now prohibited, including in sieges.
The challenges of applying the principle of distinction in sieges are principally of a practical rather than legal nature. For example, can besieging forces identify military objectives with the requisite degree of certainty? This issue is addressed in the discussion of precautions in Section III.A.1.d.
Besieging forces must identify each military objective within the besieged area and direct attacks exclusively against such objectives. The besieged area must not be considered a single military objective even though it may contain a number of such objectives. To regard the whole area as a single military objective would violate the prohibition in Article 51(5)(a) AP I, which includes among the list of indiscriminate, and therefore prohibited, attacks:
an attack by bombardment by any methods or means which treats as a single military objective a number of clearly separated and distinct military objectives located in a city, town, village or other area containing a similar concentration of civilians or civilian objects …
The rule of proportionality prohibits attacks ‘which may be expected to cause incidental loss of civilian life, injury to civilians, damage to civilian objects, or a combination thereof, which would be excessive in relation to the concrete and direct military advantage anticipated’.16
Any bombardment conducted in the context of a siege must comply with the rule. The rule applies to an ‘attack as a whole’ rather than isolated parts thereof.17 What amounts to an ‘attack as a whole’ depends on the context. If the military advantage anticipated from a single attack is not dependent on or affected by other acts, then that act is the ‘attack as a whole’ for the proportionality assessment. If, however, a particular act is an element in a larger operation where other acts contribute to the anticipated military advantage, then the operation in its entirety constitutes the ‘attack as a whole’. Setting aside for now the question of whether the rule of proportionality also applies to the entirety of a siege per se,18 examples of ‘attacks as a whole’ in siege settings include operations to prevent weapons or ammunition from entering besieged areas, or to respond to attacks from the besieged forces. The rule of proportionality requires balancing the military advantage anticipated from that operation against the incidental harm – i.e. the death of or injury to civilians and damage to civilian objects – expected from the operation, and determining whether the expected harm would be excessive in relation to the anticipated advantage.
The particularities of sieges must be taken into account when applying the rule of proportionality. The context in which an attack is conducted plays a significant role in proportionality assessments. Of particular relevance in siege situations are the limitations on movement and the isolation of the area. This is one way in which the encirclement dimension of sieges affects the application of the rule of proportionality. It affects the weight to be given in proportionality assessments to injuries to civilians and damage to civilian property. For example, injuries are likely to be harder to treat in sieges, as medical facilities may be limited and supplies stretched. Damage to civilian residences may have a more severe impact on civilians if alternative shelter is limited. If previous attacks have already damaged water treatment facilities, any further damage will be more significant than if they had been intact.
When planning or launching attacks, belligerents must take a range of precautions to spare the civilian population. These play an extremely important role in sieges. As discussed below, with regard to some of these measures belligerents are required to do what is ‘feasible’. Feasibility is understood as referring to steps that are ‘practicable or practically possible, taking into account all circumstances prevailing at the time, including humanitarian and military considerations’.19
What is considered feasible depends on the context in which an attack is planned or launched. As sieges are by nature relatively ‘static’, more significant precautions may be considered feasible for besieging forces than during more dynamic operations.
Belligerents must do everything feasible to verify that objectives against which they are directing attacks are neither civilians nor civilian objects and are not subject to special protection.20 This obligation plays an extremely important role in sieges, as civilians are likely to be in close proximity to military objectives.
IHL provides that, in case of doubt as to whether a person is a civilian, that person must be considered a civilian. Similarly, in case of doubt as to whether an object normally dedicated to civilian purposes has become a military objective, it must be assumed that it has not. This presumption of protected status is the starting point, but the required degree of certainty that an intended target of attack is indeed a military objective is unclear.21 It seems generally accepted that certainty requirements in IHL must be understood contextually. Among other things, this means that a higher degree of certainty should be demanded when an attack may have adverse consequences on civilians,22 including with regard to the verification of possible military objectives in densely populated areas, such as most besieged locations. Moreover, in view of the risk to civilians, belligerents should consider setting for themselves, as a matter of policy, higher certainty standards than those required as a matter of law.23
Belligerents must take all feasible precautions in the choice of means and methods of attack with a view to avoiding, and in any event minimizing, incidental harm.24 Key measures for doing so are the choice of weapons and the timing, location and angles of attack.25
With regard to the choice of weapons, explosive weapons with wide-area effects should be avoided in view of the significant likelihood of indiscriminate effects, and in view of the short- and long-term humanitarian effects of their use in populated areas.26
A further precaution that attackers are required to take is giving ‘effective advance warning’ of attacks that may affect the civilian population
A further precaution that attackers are required to take is giving ‘effective advance warning’ of attacks that may affect the civilian population, unless circumstances do not permit.27 In view of the close proximity of civilians to military objectives in most besieged areas, it seems unlikely that attacks into such areas would not affect civilians. Depending on the size of the besieged area, effective warnings could allow civilians to move to safer locations, or to not leave their places of shelter if they are in relative safety.
The context in which an attack is conducted affects the application of this precautionary measure. For example, the exception allowing attackers not to issue warnings ‘when circumstances do not permit’ should be interpreted narrowly in sieges. Frequently, the tempo of operations is likely to be slow, so the likelihood of attacking forces being unable to issue warnings on account of being under attack is low. However, the exception may be relevant when, for example, retaining the element of surprise could allow targeting when enemy forces are not in close proximity to civilians.
It is not just besieging forces that have obligations. Besieged forces must also take precautions to spare civilians from the effects of attacks. In particular, to the maximum extent feasible they must:
As is the case for precautions in attack, what is feasible depends on the context. Depending on the size of the besieged area and how densely populated it is, the possibilities for removing civilians from the proximity of military objectives may be limited. The second obligation may be simpler to comply with – always bearing in mind the size of the besieged area – and besieged forces can avoid locating military objects close to especially protected civilian objects such as hospitals.
While it may be challenging in practice to remove civilians from the proximity of military objectives, it is clear that besieged forces must not deliberately place civilians in proximity to military objectives to render the latter immune from attack, or to favour or impede military operations.29 It is equally clear that the fact that besieged forces may have violated this prohibition and resorted to the use of ‘human shields’ in no way absolves an attacker of its own obligations.
There is no doubt that the rules above apply to bombardments carried out during sieges. The question arises as to whether they apply also to the encirclement aspect of sieges and to sieges ‘as a whole’ – i.e. the combined effect of bombardment and encirclement.
As a matter of IHL treaty law, different rules apply to different measures taken by belligerents in the conduct of hostilities. At the most general level, during ‘military operations’ (a term that is not defined), belligerents must take constant care to spare the civilian population, civilians and civilian objects.30 The rules outlined above on targeting, including the rule of proportionality, apply to ‘attacks’, defined in Article 49 AP I as ‘acts of violence against the adversary, whether in offence or in defence’.31 Finally, some specific ‘methods of warfare’ are expressly prohibited or regulated.
It is clear that as a minimum the obligation to take constant care applies to the encirclement dimension of sieges. Whether or not the other rules also apply depends on whether encirclement and ‘sieges as a whole’ constitute ‘attacks’ for this purpose – something on which at present there is a divergence of views among writers and practitioners. Some do not consider that mere encirclement can amount to an attack, since it is not an act of violence in itself as required by Article 49 AP I. Others are of the view that, since it can be reasonably expected that the effects of encirclement will include injury or death, it should be considered an attack.32
While the rules requiring attacks to be directed at military objectives and the prohibition of indiscriminate attacks might in practice be applied to the encirclement aspect of sieges, it is difficult to see how this could be done with regard to the rule of proportionality. What would be ‘the attack as a whole’ that constitutes the frame of reference for the proportionality assessment? And while it might be feasible to identify the anticipated military advantage when planning the siege, identifying the expected incidental harm is much more difficult, as it will depend on the duration of the encirclement.
Further discussion as to whether the encirclement dimension of a siege and the siege as a whole are ‘methods of warfare’ (again a term that is undefined in the treaties) has arisen in the context of a comment of the International Court of Justice (ICJ) in the Nuclear Weapons Advisory Opinion that ‘ … methods and means of warfare, which would preclude any distinction between civilian and military targets, or which would result in unnecessary suffering to combatants, are prohibited’.33 These words are the basis for the assertion that all methods of warfare (however defined) must be discriminate and not cause unnecessary suffering. According to this view, while sieges and the starvation of combatants are not prohibited, they must nonetheless comply with the principle of distinction, so must not be applied in an indiscriminate manner that also affects and causes starvation of civilians. IHL treaty law itself, however, does not lead to the conclusion that the labelling of a particular practice as a ‘method of warfare’ has any legal consequences.34 These are complex questions that go to the heart of the structure of the rules regulating the conduct of hostilities, and in relation to which views differ.
The second set of IHL rules of relevance to sieges comprises the prohibition of the starvation of civilians as a method of warfare
The second set of IHL rules of relevance to sieges comprises the prohibition of the starvation of civilians as a method of warfare, and the rules regulating humanitarian relief operations. These are of pertinence to the encirclement aspect of sieges.
A first question is what amounts to ‘starvation’ for the purpose of the prohibition. In terms of the commodities in question, it is uncontroversial that the term ‘starvation’ must be given a broad interpretation, to encompass deprivation not just of food and water but also of other goods essential to survival in a particular context, for example heating oil and blankets.36
Does it also include the deprivation of medicines and medical equipment? Denying these to civilians can have the same severe consequences on their well-being as denial of other essential commodities. However, other rules of IHL afford greater protection by imposing more onerous obligations that require belligerents to provide such items as soon as they are necessary, rather than only once they become necessary in order to prevent or alleviate the degree of suffering and deprivation that amounts to starvation. It is a foundational principle of IHL that wounded and sick civilians and fighters are entitled to receive to the fullest extent practicable, and with the least possible delay, the medical care and attention required by their condition. In view of this entitlement, if there are people in need of such care who are not receiving it, besieging and besieged forces must accept offers to provide the necessary assistance in a principled manner, and allow and facilitate rapid and unimpeded passage of medical supplies and equipment.37
In terms of threshold of need, ‘starvation’ implies a high degree of deprivation, more significant than the ‘not adequately provided’ standard that brings into play the rules of IHL regulating humanitarian relief operations.38 However, it is not necessary for deaths to occur.
A second and more complex question is whether the prohibition is limited to situations where a belligerent deliberately starves civilians, or whether it also covers situations where, although not intended, the starvation of civilians is the foreseeable consequence of a particular course of action. If a besieged area holds fighters and civilians, would a besieging party that does not allow the entry of commodities because it wants to starve the fighters, knowing that this is also going to starve civilians, be violating the prohibition? Is what matters the intention underlying a course of action or its effects?
One view, based on the wording of the prohibition in Article 54 AP I and, in particular, on its framing of the practice ‘as a method of warfare’, is that only the deliberate starvation of civilians is prohibited.39 A number of military manuals appear to support this interpretation.40 Additional support for this narrow interpretation comes from the wording of Article 54(2) AP I, which sets out an example of a violation of the prohibition of starvation, and refers to the destruction of objects indispensable to the survival of the civilian population ‘for the specific purpose of denying them for their sustenance value to the civilian population’ (emphasis added).
Some others consider that while the prohibition covers only the deliberate starvation of civilians, measures that may have the ‘incidental’ effect of causing the starvation of civilians – including operations to starve fighters, such as sieges – must not be disproportionate: i.e. the anticipated military advantage of such measures must not be excessive in relation to the civilian deaths or injuries (including from starvation) that they may be expected to cause.41 This approach has to rely on the claim discussed above42 that the mere encirclement of an area constitutes an ‘attack’, bringing the rule of proportionality into play; as indicated above, that is a difficult argument to make.43
A further view is that all methods of warfare must, as highlighted by the ICJ in the Nuclear Weapons Advisory Opinion, comply with the principle of distinction.44 While the starvation of fighters as a method of warfare is permissible, it must not be applied in a manner that is indiscriminate. If belligerents resort to the starvation of fighters, they must not do so in a manner that is indiscriminate and also causes the starvation of civilians.
Whatever position is adopted with regard to the scope of the prohibition of starvation, the rules regulating humanitarian relief operations outlined in the next section will become applicable whenever civilians are inadequately provided with goods essential to their survival. If respected, these rules will prevent starvation from occurring.
The rules of IHL regulating humanitarian relief operations play an extremely important role in alleviating the impact on civilians of the encirclement and isolation of sieges. They are of particular significance in view of the current divergence of views as to the scope of the prohibition of starvation of civilians as a method of warfare and also because, as already noted, these rules come into play when civilians are facing a lower level of deprivation than ‘starvation’.
Primary responsibility for meeting the basic needs of civilians lies with the party that has effective control over them – in the case of sieges, the besieged party. If civilians are not adequately provided with food, water, medical supplies, clothing, means of shelter, heating fuel and other supplies essential to their survival, and if humanitarian relief operations are already being conducted in the state where the siege is occurring, besieging and besieged forces must allow and facilitate the rapid and unimpeded passage of humanitarian relief operations. Both sides are entitled to adopt measures of control such as searches of the relief consignments.45
Humanitarian relief is intended solely for civilians, and ideally besieged and besieging parties should agree upon arrangements to monitor distributions in besieged areas. As it might be difficult to reach agreement, besieged forces are also likely to benefit from the relief consignments, either directly or indirectly as the entry of relief reduces the number of people dependent on commodities already within the besieged areas – i.e. it ‘frees up’ available supplies in the besieged areas for fighters.
In practice, this obligation to allow civilians to receive relief will limit the extent to which one key dimension of sieges – the isolation of enemy forces – can be imposed. Consequently, it reduces the effectiveness of the siege.
The third set of rules relevant to sieges consists of those relating to evacuations and their interplay with the prohibition of forced displacement. Evacuations can be a way of striking a balance between the military aims pursued in sieges and belligerents’ obligations towards civilians.
Three of the four IHL treaty provisions that specifically refer to besieged areas relate to evacuations
Removing the civilian population from besieged areas ends their exposure to hostilities and to the deprivations associated with sieges. It is therefore not surprising that three of the four IHL treaty provisions that specifically refer to besieged areas relate to evacuations. The virtually identical provisions of the First, Second and Fourth Geneva Conventions foresee the possibility for belligerents to conclude agreements for the evacuation of the wounded and sick on land or at sea, or of particularly vulnerable members of civilian populations from besieged or encircled areas respectively.46 Although not specifically mentioned in the provisions on precautions, evacuations of civilians from besieged areas are a way of giving effect to the general obligation in the conduct of military operations to take constant care to spare the civilian population.47
As far as the besieging party is concerned, it is clear that the prohibition on directing attacks against civilians precludes firing on civilians who are fleeing from the besieged area.48 For the besieged party, evacuating civilians could be a way of discharging the obligation to ‘take the other necessary precautions to protect the civilian population, individual civilians and civilian objects under their control against the dangers resulting from military operations’.49 Depending upon the size of the besieged area, failure by the besieged party to allow civilians to leave could amount to a violation of the prohibition on using the presence of civilians to shield military objectives from attacks or impede military operations.50
Besieged and besieging parties are entitled to impose conditions on evacuations. These conditions may specify which categories of people are entitled to participate, and may include measures such as searches to ensure weapons or other military materials are not being removed, as well as oversight arrangements for the agreed-upon modalities.
From the point of view of civilians, the departure from the besieged areas must be voluntary, informed, and conducted in safety, during both the actual evacuation and the subsequent arrangements for shelter. Civilians who do not participate in evacuations and who remain in besieged areas do not forfeit their status and protections. Hostilities cannot be conducted on the presumption that anyone who chose not to be evacuated is a fighter, and the rules regulating humanitarian relief operations continue to apply for the benefit of civilians who have remained.
Evacuations can be life-saving for besieged civilians. Nonetheless, doubts have been raised as to the compatibility of evacuations with the prohibition on forcible displacement of civilian populations. The Syria Commission of Inquiry concluded that the evacuation of eastern Aleppo in December 2016 constituted a war crime.51 This sweeping conclusion fails to take into account the exception to the prohibition, allowing total or partial evacuation of a given area if the security of the population or imperative military reasons so demand.52 While the conclusion was an incorrect interpretation of the law, it does highlight the close relationship that may exist between evacuations and policies of forced displacement and ethnic cleansing. Evacuations must be temporary, and displaced people must be allowed to return as soon as the reasons for their displacement cease to exist.
