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War Watch
Legal Explainers

Rules on the Conduct of Hostilities

International humanitarian law provides a detailed framework to govern the conduct of hostilities (traditionally known as “Hague law”). Additional Protocols I and (albeit to a more limited extent) II to the 1949 Geneva Conventions set forth detailed rules in relation to, respectively, international and non-international armed conflicts. Many of these provisions are also considered reflecting rules of customary international law applicable in both types of armed conflict.

Principle of distinction

According to the fundamental principle of distinction, parties to an armed conflict must at all times distinguish between civilian persons and objects, on the one hand, and combatants/fighters and military objectives, on the other hand.1 Art 48 AP I; Art 13 AP II; ICRC, Customary IHL Rule 1: ‘The Principle of Distinction between Civilians and Combatants’, https://ihl-databases.icrc.org/en/customary-ihl/v1/rule1; ICRC, Customary IHL Rule 7: ‘The Principle of Distinction between Civilian Objects and Military Objectives’, https://ihl-databases.icrc.org/en/customary-ihl/v1/rule7. Attacks (defined as acts of violence against the adversary, whether in offence or in defence)2 Art 49(1) AP I. may only be directed at the latter targets.3 Arts 52(2) AP I; ICRC, Customary IHL Rule 1: ‘The Principle of Distinction between Civilians and Combatants’, https://ihl-databases.icrc.org/en/customary-ihl/v1/rule1; ICRC, Customary IHL Rule 7: ‘The Principle of Distinction between Civilian Objects and Military Objectives’, https://ihl-databases.icrc.org/en/customary-ihl/v1/rule7.

Civilians shall be protected against the dangers arising from military operations, unless and for such time as they take a direct part in hostilities.4 Art 51(1) and (3); Art 13(3) AP II; ICRC, Customary IHL Rule 6: ‘Civilians’ Loss of Protection from Attack’, https://ihl-databases.icrc.org/en/customary-ihl/v1/rule6. The civilian population as such, as well as persons hors de combat, shall not be the object of attack,5 See notably Arts 51(2) AP I and Art 13(2) AP II for the civilian population, and Art 3 GCs, Art 41(1) AP I, and ICRC, Customary IHL Rule 47: ‘Attacks against Persons Hors de Combat’, https://ihl-databases.icrc.org/en/customary-ihl/v1/rule47 for persons hors de combat. and indiscriminate attacks are prohibited.6 Art 51(4) AP I; ICRC, Customary IHL Rule 11: ‘Indiscriminate Attacks’, https://ihl-databases.icrc.org/en/customary-ihl/v1/rule11. Acts or threats of violence the primary purpose of which is to spread terror among the civilian population are similarly prohibited.7 Art 51(2) AP I; Art 13(2) AP II; ICRC, Customary IHL Rule 2: ‘Violence Aimed at Spreading Terror among the Civilian Population’, https://ihl-databases.icrc.org/en/customary-ihl/v1/rule2. In case of doubt whether a person is civilian or not, they shall be presumed to be so.8 Art 50(1) AP I.

A civilian object is any object that is not a military objective.9 Art 52(1) AP I; ICRC, Customary IHL Rule 9: ‘Definition of Civilian Objects’, https://ihl-databases.icrc.org/en/customary-ihl/v1/rule9. A military objective is an object that by its nature, location, purpose or use makes an effective contribution to military action, and whose destruction, capture or naturalization offers a definite military advantage.10 Art 52(2), AP I; ICRC, Customary IHL Rule 8: ‘Definition of Military Objectives’, https://ihl-databases.icrc.org/en/customary-ihl/v1/rule8 Whereas civilian objects can become legitimate targets if these conditions are met, the loss of protection from attack persists only for such time as they qualify as military objectives. In case of doubt, there is a presumption against loss of protection for objects normally dedicated to civilian purposes.11 Art 52(3) AP I

Proportionality

When targeting a military objective, a party to an armed conflict must respect the IHL proportionality rule. This rule prohibits the launching of attacks that 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.12 Arts 51(5)(b) and 57 AP I; ICRC, Customary IHL Rule 14: ‘Proportionality in Attack’, https://ihl-databases.icrc.org/en/customary-ihl/v1/rule14 The evaluation must be made ex ante, from the perspective of the attacker.

Precautions in and against the effects of attack

Underpinning the rules of distinction and proportionality is the duty to take precautionary measures in attack. This comprises, among others, the duty to take all feasible measures to verify that the target is lawful to attack, to select means and methods of warfare that minimize the risk to civilians, and to provide effective advance warning if circumstances allow. Those duties apply to those who plan, decide and/or carry out the attack.13 Art 57 AP I; ICRC, Customary IHL Rules 15–21.

There is a further duty on all parties to the conflict to take all feasible precautions to protect civilians and civilian objects under their control against the effects of attacks. Such measures include, where possible, evacuating areas containing military objectives of civilians and removing civilian objects from the vicinity of military objectives; avoiding locating military objectives in or near densely populated areas; and taking other precautions to protect civilians and civilian objects from the dangers of military operations.14 Art 58 AP I; ICRC, Customary IHL Rules 22–24. Note however that the application of Rules 23 and 24 also in the context of NIACs is qualified by the term ‘arguably’ in the ICRC Commentary

Persons and objects enjoying specific protection

In addition to the general rules on protection from attack outlined above, IHL sets forth specific protection in relation to various categories of persons and objects.

Medical personnel and units

Medical and religious personnel must be respected and protected in all circumstances, and only lose their protection if they commit, outside their humanitarian function, acts harmful to the enemy.15 See Arts 24–26 GC I, Art 36 GC II, Art 20(1) GC IV, Art 15(1) AP I, Art 9(1) AP II and ICRC, Customary IHL Rule 25: ‘Medical Personnel’, https://ihl-databases.icrc.org/en/customary-ihl/v1/rule25 for medical personnel; and Art 24 GC I, Art 36 GC II, Art 15(5) AP I, Art 9(1) AP II and ICRC, Customary IHL Rule 27: ‘Religious Personnel’, https://ihl-databases.icrc.org/en/customary-ihl/v1/rule27 for religious personnel With regard to objects, also medical units (such as hospitals and medical depots) and medical transport must be respected and protected in all circumstances, provided they are assigned exclusively to medical purposes.16 Arts 19, 20–22 and 35–36 GC I; Arts 22, 24–35 and 38 GC II; Arts 18–19 and 21–22 GC IV; Arts 8, 12, 21–23 and 25–28 AP I; Art 11 AP II; ICRC, Customary IHL Rule 28: ‘Medical Units’, https://bit.ly/4mdpd82; ICRC, Customary IHL Rule 29: ‘Medical Transports’, http://bit.ly/4n8KMGO The protection of medical units and transports would only cease for such time as they are used to commit acts harmful to the enemy, outside their humanitarian function.17 Arts 21–22 GC I; Art 19 GC II; Art 13 AP I; Art 11(2) AP II; ICRC, Customary IHL Rule 28: ‘Medical Units’, https://ihl-databases.icrc.org/en/customary-ihl/v1/rule28; ICRC, Customary IHL Rule 29: ‘Medical Transports’, https://ihl-databases.icrc.org/en/customary-ihl/v1/rule29 Moreover, even if this were to happen, the protection is only lost after a warning has been given that sets, whenever appropriate, a reasonable time-limit, and only after such warning has remained unheeded.18 Arts 21-22 GC I; Arts 34-35 GC II; Art 13(1) AP I ; Art 11(2) AP II. See also ICRC, Customary IHL Rule 25: ‘Medical Personnel’, https://ihl-databases.icrc.org/en/customary-ihl/v1/rule25, which does not include the latter part. Once the special protection is lost, the general rules on the conduct of hostilities apply.

Works and installations containing dangerous forces

The protection afforded to works and installations containing dangerous forces reflects the concern for the dangers arising from their damage or destruction. Thus, dams, dykes and nuclear power stations (as well as other objects located at or in the vicinity of these works or installations) are protected from attack even when they qualify as military objective, if the attack may cause the release of dangerous forces and consequent severe losses among the civilian population.19 Art 56(1) AP I; Art 15 AP II It is only under very specific circumstances that these objects may lose protection from attack – i.e., if they are used for other than its normal function and in regular, significant and direct support of military operations, and if the attack is the only feasible way to terminate such support.20 Art. 56(2) AP I; ICRC, Customary IHL Rule 42: ‘Works and Installations Containing Dangerous Forces’, https://ihl-databases.icrc.org/en/customary-ihl/v1/rule42 Parties to armed conflict also have stricter precautionary obligations to avoid releasing dangerous forces.21 Art 56(3) and (5)–(6) AP I

The natural environment

Over time, IHL has come to protect the natural environment as such, and not only as a result of the application of the general rules protecting civilian objects. Therefore, parties to an armed conflict must pay due regard to the natural environment in the conduct of their military operations.22 ICRC, Customary IHL Rule 44: ‘Due Regard for the Natural Environment in Military Operations’, https://ihl-databases.icrc.org/en/customary-ihl/v1/rule44 (which according to the ICRC applies in IACs and ‘arguably’ also in NIACs) In particular, they cannot use methods or means of warfare that are intended, or may be expected, to cause widespread, long-term and severe damage to the natural environment (thereby prejudicing the health or survival of the population),23 Arts 35(3) and 55(1) AP I; ICRC, Customary IHL Rule 45: ‘Causing Serious Damage to the Natural Environment’, https://ihl-databases.icrc.org/en/customary-ihl/v1/rule45 (which according to the ICRC applies in IACs and ‘arguably’ also in NIACs) nor can they use the destruction of the natural environment as a weapon.24 Arts I–II, 1976 Convention on the Prohibition of Military or Any Other Hostile Use of Environmental Modification Techniques; ICRC, Customary IHL Rule 45: ‘Causing Serious Damage to the Natural Environment’, https://ihl-databases.icrc.org/en/customary-ihl/v1/rule45 (which according to the ICRC applies in IACs and ‘arguably’ also in NIACs)

Cultural property

Similarly, cultural property also enjoys specific protection in addition to that to which civilian objects are generally entitled.25 For a definition of cultural property, see Art 1(1), 1954 Hague Convention for the Protection of Cultural Property in the Event of Armed Conflict The obligation to respect cultural objects entails two aspects: an obligation to refrain from any use of cultural property and its immediate surroundings for purposes which are likely to expose it to destruction or damage in the event of armed conflict; and an obligation to refrain from any act of hostility (including attacks) directed against such property.26 Art 4(1), 1954 Hague Convention; ICRC, Customary IHL Rule 38: ‘Attacks Against Cultural Property’, https://ihl-databases.icrc.org/en/customary-ihl/v1/rule38; ICRC, Customary IHL Rule 39: ‘Use of Cultural Property for Military Purposes’, https://ihl-databases.icrc.org/en/customary-ihl/v1/rule39 These obligations could only be waived in case of imperative military necessity27 Art 4(2), 1954 Hague Convention; Art 6, 1999 Second Protocol to the 1954 Hague Convention; ICRC, Customary IHL Rule 38: ‘Attacks Against Cultural Property’, https://ihl-databases.icrc.org/en/customary-ihl/v1/rule38; ICRC, Customary IHL Rule 39: ‘Use of Cultural Property for Military Purposes’, https://ihl-databases.icrc.org/en/customary-ihl/v1/rule39 – except for historic monuments, works of art or places of worship which constitute the cultural or spiritual heritage of mankind, which would be protected in all circumstances.28 Art 53(a)–(b) AP I; Art 16 AP II; see also commentary to ICRC, Customary IHL Rules 38 and 39