Introduction
The regulation of state-sanctioned violence, particularly the use of weapons, has traditionally been viewed through two distinct legal lenses: international humanitarian law (IHL), the law of armed conflict, and international human rights law (IHRL), which governs a state’s obligations towards individuals. The ‘instinctive’ view, as noted by Casey-Maslen, is that IHL is the sole arbiter of legality during armed conflict (Casey-Maslen, 2015). However, the increasing complexity of modern conflicts and security operations has challenged this neat division. This essay will critically reflect on the relationship between these two bodies of law. It will be argued that while their concurrent application can provide greater and complementary safeguards, particularly concerning absolute prohibitions like torture, it can also create significant disadvantages in the form of legal uncertainty, especially in the regulation of lethal force. The protections offered are therefore not uniformly greater, but differ in scope and standard, leading to a complex interaction with both advantages and drawbacks depending on the specific scenario.
The Traditional Separation and Modern Convergence
Traditionally, IHL and IHRL were seen as occupying separate spheres. IHL, also known as the law of armed conflict or jus in bello, applies specifically during situations of armed conflict, whether international or non-international. Its primary purpose is to regulate the conduct of hostilities by balancing military necessity with humanitarian considerations. Key IHL principles include distinction (distinguishing between combatants and civilians), proportionality (ensuring an attack is not excessive in relation to the military advantage gained), and precaution (taking all feasible precautions to avoid civilian harm).
In contrast, IHRL applies at all times, in peace and in war. It governs the relationship between a state and individuals within its jurisdiction. It establishes fundamental rights, such as the right to life and the prohibition of torture, which states are obliged to respect and ensure. The traditional view was that during an armed conflict, the specific rules of IHL would apply as lex specialis (the special law), displacing the more general rules of IHRL.
However, the International Court of Justice (ICJ) has decisively rejected a simple displacement model. In its advisory opinion on the Legality of the Threat or Use of Nuclear Weapons, the ICJ affirmed that the protection of IHRL does not cease in times of armed conflict. It held that the right to life, for instance, continues to apply, but that what constitutes an arbitrary deprivation of life must be interpreted by reference to the applicable lex specialis, namely IHL (ICJ, 1996, para 25). This established a co-application model, where IHRL remains the background norm, and IHL provides the specific framework for assessing conduct during hostilities. This model of co-application is where both the advantages and disadvantages of their interaction become apparent.
Weapons Law: Differing or Greater Safeguards?
The regulation of weapons provides a clear example of the differing standards between IHL and IHRL. IHL governs the ‘means and methods of warfare’ and prohibits weapons that are inherently indiscriminate or are of a nature to cause superfluous injury or unnecessary suffering (Additional Protocol I, 1977, Art 35). The focus is on the weapon's effects in a combat scenario against legitimate military targets.
IHRL, on the other hand, regulates the use of force through the lens of the right to life. Under instruments like the European Convention on Human Rights (ECHR) and the International Covenant on Civil and Political Rights (ICCPR), lethal force by state agents is a measure of last resort, permissible only when ‘absolutely necessary’ to protect life (McCann and Others v UK, 1995). This is a far stricter standard than the IHL principle of proportionality in an attack.
The application of these differing standards provides distinct advantages in law enforcement contexts. In situations of riots or internal disturbances that do not amount to an armed conflict, IHRL is the sole applicable framework. This ensures that lethal force is tightly restricted and that law enforcement must prioritise non-lethal means and arrest over killing. The use of a firearm, for example, must be strictly necessary to counter an imminent threat of death or serious injury.
However, in the 'grey zones' of contemporary conflict, such as counter-terrorism operations or low-intensity non-international armed conflicts, applying both regimes creates complexity. When a state targets a member of an organised armed group in a populated area, does the IHL targeting paradigm apply, or the IHRL ‘absolute necessity’ standard? The IHRL framework could be seen as offering 'greater' protection to individuals by requiring the state to attempt capture rather than kill, even if the individual is a legitimate military target under IHL. This has been a key argument of human rights bodies. The advantage is enhanced protection for life. The disadvantage, however, is the significant legal and operational uncertainty it creates for soldiers, who must make split-second decisions based on complex legal tests. This ambiguity can undermine legal certainty and potentially hinder effective military operations against hostile actors, who themselves rarely abide by any legal constraints.
Torture and Sexual Violence: A Complementary Shield
In contrast to the tensions in weapons law, the prohibition of torture and sexual violence is an area where IHL and IHRL are highly complementary, and their joint application provides unequivocally greater safeguards. Both legal frameworks contain an absolute and non-derogable prohibition of torture. Common Article 3 to the four Geneva Conventions (1949) forbids ‘cruel treatment and torture’ in non-international armed conflicts, a prohibition that is considered customary international law. Similarly, IHRL instruments like the UN Convention against Torture (1984) and regional treaties like the ECHR (Art 3) establish an absolute ban on torture and inhuman or degrading treatment or punishment, from which no derogation is permitted, even in times of public emergency.
Here, there is no lex specialis rule in IHL that would displace the IHRL norm. Instead, the two regimes reinforce each other. The advantage of their concurrent application is the creation of a multi-layered system of protection and accountability. IHL classifies torture as a grave breach or a war crime, establishing a basis for individual criminal responsibility before international tribunals like the International Criminal Court. IHRL, meanwhile, provides more detailed jurisprudence on what constitutes torture and creates monitoring bodies (like the Committee against Torture) and judicial mechanisms (like the European Court of Human Rights) through which individuals can seek redress from states.
A similar dynamic exists for the prohibition of sexual violence. IHL explicitly prohibits ‘rape, enforced prostitution, and any form of indecent assault’ as grave breaches and war crimes (Additional Protocol I, 1977, Art 76; Rome Statute, Art 8). IHRL also protects against sexual violence through the right to be free from inhuman treatment and the right to physical integrity. Applying both frameworks provides distinct advantages: IHL provides for criminal accountability for perpetrators in conflict, while IHRL imposes a ‘due diligence’ obligation on states to prevent, investigate, and punish such acts, ensuring a more comprehensive approach to protection and justice that extends beyond the conduct of hostilities.
The Disadvantages of Concurrent Application
While the complementarity of IHL and IHRL is beneficial in some areas, the primary disadvantage of their overlapping application is the potential for legal confusion and the dilution of IHL as a pragmatic body of law. As discussed in the context of weapons law, forcing soldiers to apply a law enforcement paradigm (IHRL) in a combat environment (IHL) can be unworkable. The IHL framework acknowledges that in an armed conflict, the killing of enemy combatants is a legitimate act of war, not a deprivation of life to be justified by ‘absolute necessity’. Applying an IHRL standard could arguably place state forces at a severe tactical disadvantage against non-state armed groups that do not operate under similar constraints.
Furthermore, critics argue that the ‘humanisation’ of conflict through the importation of IHRL norms risks undermining the specific balance struck by IHL between military necessity and humanity (Sassòli, 2006). IHL is designed to be a realistic framework that can be applied by armed forces in the chaos of battle. Over-complicating this with a second, and at times contradictory, legal standard may make compliance less likely, potentially leading to worse outcomes for civilians if the law is seen as impractical and is disregarded altogether. The ICJ’s judgment in Armed Activities on the Territory of the Congo confirmed that both bodies of law could apply concurrently, but it offered limited practical guidance on how to resolve direct conflicts between their standards for the use of force, leaving the issue largely to academic debate and the practice of states and human rights tribunals (ICJ, 2005).
Conclusion
In conclusion, the relationship between international human rights law and international humanitarian law is not one of simple hierarchy or mutual exclusion. The assertion that IHRL provides an overarching legal framework for weapons use is indeed a departure from traditional views, but it reflects the reality of modern security challenges. The protections offered by both disciplines when applied together are not uniformly 'greater', but are certainly 'differing', and this creates both advantages and disadvantages.
In areas of absolute prohibition, such as torture and sexual violence, the two legal regimes are complementary, creating a robust and multi-layered shield that reinforces protection and enhances accountability. This is a distinct advantage of their co-application. However, in regulating the use of lethal force, the differing standards of IHL’s proportionality and IHRL’s absolute necessity create significant tension. While the IHRL standard offers a higher threshold of protection for the right to life, it introduces legal uncertainty and operational challenges that can be a considerable disadvantage in armed conflict scenarios. Ultimately, while the trend towards viewing the two bodies of law as complementary is a positive development for human protection, the key challenge remains in clarifying their precise interaction to ensure that the law provides clear guidance and remains a practical tool for regulating violence, rather than an abstract and unworkable ideal.
References
Additional Protocol I (1977) Protocol Additional to the Geneva Conventions of 12 August 1949, and relating to the Protection of Victims of International Armed Conflicts.
Casey-Maslen, S. (2015) ‘Weapons Under International Human Rights Law’. In: Casey-Maslen, S. (ed.) Weapons Under International Human Rights Law. Cambridge University Press, pp. 1-28.
Convention against Torture and Other Cruel, Inhuman or Degrading Treatment or Punishment (1984) (UNCAT).
European Convention on Human Rights (1950) (ECHR).
Geneva Conventions (1949) I-IV.
International Court of Justice (1996) Legality of the Threat or Use of Nuclear Weapons, Advisory Opinion, ICJ Reports 1996, p. 226.
International Court of Justice (2005) Armed Activities on the Territory of the Congo (Democratic Republic of the Congo v. Uganda), ICJ Reports 2005, p. 168.
International Covenant on Civil and Political Rights (1966) (ICCPR).
McCann and Others v The United Kingdom (1995) App no 18984/91, 21 EHRR 97.
Rome Statute of the International Criminal Court (1998).
Sassòli, M. (2006) ‘Transposition of International Humanitarian Law into Domestic Law’. In: Haug, H. and Gasser, H-P. (eds.) Humanity for All: The International Red Cross and Red Crescent Movement. Paul Haupt Publishers, pp. 565-598.
