Analysis of the Advisory Opinion on the Legality of the Threat or Use of Nuclear Weapons


When the US dropped two atomic bombs on Hiroshima and Nagasaki in 1945, Japan unconditionally surrendered to the US. This led many states to witness the unique significance of nuclear weapons. For this reason, many states began to develop their nuclear arsenals. Bearing this in mind, the World Court Project, a civil society campaign throughout the early 90s, aimed to secure an Advisory Opinion of the International Court of Justice to settle the legal status of nuclear weapons. Their efforts were successful when the United Nations General Assembly (UNGA) passed a resolution requesting the International Court of Justice (ICJ) to render an opinion on whether the threat or use of nuclear weapons in any circumstance is permitted under international law. 

Notably, the resolution to request an advisory opinion requires a simple majority of ‘members present and voting.’ In the case at hand, it was passed by a slight majority of 78 to 43, with 38 abstentions. This further indicates the disagreement of the international community on whether an advisory opinion on such a matter should be sought from the ICJ. On 20 December 1994, the same was communicated to the registrar of the Court. After receiving the written submissions and hearing oral pleadings, the Court gave its advisory opinion on 8 July 1996.

Jurisdiction and the Question asked

At the outset, some states argued that the General Assembly could only ask a question about its scope, given under the UN Charter. In response, the Court noted that the scope of the General Assembly is not limited and extends to any question about international law. Support for such a view was found in Article 10, mandating the UNGA to discuss any matter falling in the scope of the Charter, and Article 96(1), authorizing the UNGA to seek an advisory opinion from the ICJ on any legal question.  Besides that, some states, like the United States and the Netherlands, also argued that the question posed before the Court is abstract and the Court should not answer it. Furthermore, the aforementioned states argued that if an advisory opinion were sought, it would halt the progress already made within the nuclear law regime. Despite these pleas, the Court proceeded with an advisory opinion on the matter. 

During their written and oral submissions, some states also objected to the wording used by the General Assembly. Their main contention was that the General Assembly should have used ‘prohibited’ instead of ‘permitted’ while asking about nuclear weapons because only the express prohibition in either treaty or customary law would bind the states not to act in a certain manner.  Support for such a view was found in the Lotus case of the Permanent Court of International Justice, wherein the Court had stated that in international law, ‘restrictions upon the states cannot be presumed;’ rather, restrictions must be expressed in clear terms, ideally in treaty language. This implies that their right to use nuclear weapons remains absolute without any specific prohibition. However, in its advisory opinion, the Court declared that the use of ‘permitted’ in the question asked is of no significance since the legal conclusions to be drawn from this are of no relevance.

Where the Court considered the use of ‘permitted’ of no relevance, President Bedjaoui, in his separate declaration, stated that the ‘resolutely, positivist, voluntary approach of international law which still held sway at the beginning of the century has been replaced by an objective conception of international law.’ In his view, owing to the advancement of the ‘international community’, concepts such as ‘jus cogens‘ and ‘erga omnes’ have been developed over time, dictating the universal obligation of international law. Therefore, the Lotus principle requiring consent as a commitment needs to be looked at afresh. For him, a state may be held liable even if it has not consented to a norm through a treaty. 

Ascertaining the relevant law

In its advisory opinion, the Court examined the rules pertaining to the law of armed conflict and the law relating to the use of force under the UN Charter. However, before analyzing what the Court had to say about the aforementioned regimes, it is pertinent to shed some light on how the Court reached such a conclusion. 

During the oral proceedings, many states submitted that nuclear weapons are expressly prohibited under international human rights law, namely Article 6 of ICCPR since it prohibits the arbitrary deprivation of life. However, in its advisory opinion, the Court stated that even if ICCPR talks about ‘arbitrary deprivation of life,’ what constitutes ‘arbitrary’ through ‘ a use of a certain weapon in warfare’ is to be determined by lex specialis, which, in the present case, is the law of armed conflict. 

In addition, some states also submitted that since the use of nuclear weapons would also result in the loss of a large population, it would amount to genocide. However, the Court, in its advisory opinion, stated that for genocide to occur, it would require dolus specialis, an intent to destroy a certain group on racial, ethnic, national, or religious grounds. Such a view is consistent with the jurisprudence of international tribunals, in particular, the International Criminal Tribunal for Rwanda, and the definition of genocide later adapted under the Rome Statute. Ultimately, it can be stated that the Court remained reluctant to accept that the prohibition of nuclear weapons can be found in the corpus of human rights law and the law of genocide.

International humanitarian law

During oral proceedings, many states submitted that nuclear weapons should be considered ‘poisoned weapons’. In such a case, they would be prohibited under both the Second Hague Declaration of 29 July 1899 and the Hague Regulations Respecting the Laws and Customs of War on Land annexed to the Hague Convention IV, prohibiting poisoned weapons. In response, the Court noted that no consensus exists on what the terms ‘poison’ or ‘poisoned weapons’ mean. In such a case, only the weapons ‘whose prime, or even exclusive, effect is to poison or asphyxiate’ be considered poisoned weapons. Therefore, nuclear weapons cannot be deemed to be prohibited on this line of reasoning.  

Having not found any express prohibition of the use of nuclear weapons in the treaty law relating to armed conflict, the attention of the Court was brought to the cardinal principles governing customary IHL. The Court noted two cardinal principles of customary IHL as applying to the legality of nuclear weapons.  The first principle is the principle of distinction, which prohibits indiscriminate attacks in an armed conflict, and the second is the principle of unnecessary suffering, prohibiting state parties not to cause unnecessary suffering to combatants.  

Owing to this, the Court held that the use of nuclear weapons ‘in fact seems scarcely reconcilable with respect to such requirements’ under IHL. However, the Court stated that it cannot conclude ‘with certainty that the use of nuclear weapons would necessarily be at variance with the principles and rules of law applicable in armed conflict in any circumstance.’ 

This reasoning of the Court warrants three comments. Firstly, in its advisory opinion, the Court did mention the principle prohibiting indiscriminate attacks but failed to consider the principle of proportionality. Where the former urges the state to make a distinction between military targets and civilian population, the latter urges not to cause loss to the civilian population or damage to civilian objects that is in excess to the overall military advantage anticipated.’ Simply put, the principle of proportionality only comes into play when a military advantage is to be assessed in light of anticipated civilian loss. Therefore, the Court should have also stated that whenever a state resorts to nuclear weapons for military advantage, its anticipated effects on civilian life should not be disproportionate to the military advantage sought. Had the Court done so, it would have been a more consistent and comprehensive application of international humanitarian law.  

Secondly, instead of outrightly stating that it cannot conclude with certainty, the Court should have made an analysis on the scenarios in which a nuclear weapon can be used without violating the principles of distinction and unnecessary suffering. One such scenario was mentioned by the US during the oral proceedings, stating that ‘in some cases, such as the use of a low yield nuclear weapon against warships on the High Seas or troops in sparsely populated areas, it is possible to envisage a nuclear attack which caused comparatively few civilian casualties.’

In response, Judge Shahabuddeen, in his dissenting opinion, noted that ‘the eleventh preambular paragraph of the 1968 [Nuclear Non-Proliferation Treaty], which was extended “indefinitely” in 1995, records that the States parties desired the ‘liquidation of all their existing stockpiles and the elimination from national arsenals of nuclear weapons.’ He further elaborated that this prohibition is to be applied to all nuclear weapons. Therefore, no exception to the tactical and low-yield nuclear weapons used in a desert or against any warship exists under international law. However, no such reasoning was made by the Court in its advisory opinion. Unlike Justice Shahabuddeen,  the majority did not draw an analysis and left the matter uncertain. I argue that such an analysis would surely have required a value judgment but would have been beneficial for those seeking any clear answer on the matter.

Thirdly, even if we assume that there might be a case when nuclear weapons may be used in conformity with the aforementioned principles, it is very hard to imagine that, even in such scenarios, there would not be severe effects on the environment. As per Article 35(3) of the AP I, it is prohibited to cause widespread (requiring an area of several hundred square kilometers), long-term (requiring a time period of several decades), and severe (requiring serious disruption to human life) damage to the natural environment. One may argue that it is very unlikely to meet these requirements, particularly where a low-yield tactical nuclear weapon has been used. However, the Court should have, at least, stated that a state employing nuclear weapons must also meet the criteria laid in article 35(3) and 55 of AP I. Had the Court done so, the scenarios in which nuclear weapons can be used would have been reduced further.

Put simply, it can be stated that the Court was correct to conclude that there existed no express prohibition of the use of nuclear weapons in both the treaty and customary IHL. However, as mentioned earlier, the Court falls short of acknowledging the gravity of the question posed. For instance, it failed to analyze the situations in which a state may use nuclear weapons in conformity with the cardinal principles of IHL. Besides that, the Court also failed to introduce the principle of proportionality and how seriously the use of nuclear weapons may affect the environment.  

The Law relating to the use of force

During the oral proceedings, the Court also considered whether the law relating to the use of force, enshrined under the UN Charter, prohibits the use of nuclear weapons. In its advisory opinion, the Court noted that any use of force might become lawful if it falls under Article 51 of the UN Charter. This further implies that if the requirements of necessity and proportionality under customary international law on the use of force are met, the use of nuclear weapons may become lawful. 

Some states submitted that owing to the nature of nuclear weapons, there must be a strong risk of devastation involved to meet the requirements of necessity and proportionality. In other words, the threshold of necessity and proportionality must remain high in the case of nuclear weapons. For instance, would a state be justified in using nuclear weapons in self-defence if it has already been used against it? Here, it is necessary to justify both the necessity to use nuclear weapons and the extent to which they have been used. 

Regarding both, Malcolm Shaw asserts that there is no precise definition. Therefore, it will depend on the circumstances of each case. In other words, the necessity to use nuclear weapons against major cities of an enemy state in self-defense may not be justified if the victim state has been targeted with only a low-yield nuclear weapon. Furthermore, such an attack is also unlikely to meet the requirement of proportionality. In my opinion, the Court remained silent on how high the criteria may be set. Considering the risk involved in using nuclear weapons, the Court should have laid down criteria to which the states may rely whenever they intend to resort to nuclear weapons in self-defense. 

Treaty law relating to Nuclear weapons

Besides IHL and the law on the use of force, the attention of the Court was also brought to the treaties expressly prohibiting the use of nuclear weapons. While looking for an express prohibition of the use of nuclear weapons in the Nuclear Non-Proliferation Treaty and the Treaty of Tlatelolco, the Court concluded that even if many states have consented to the Treaty of Tlatelolco, the prohibition cannot be considered absolute. The reason is that nearly all the nuclear weapon states, while consenting to the respective treaties, reserved the right to use nuclear weapons in exceptional circumstances, particularly if an armed attack has been made against their territory. In the same vein, the Court also concluded that, while signing the Nuclear Non-Proliferation Treaty, many nuclear weapon states reserved the right to use nuclear weapons if a non-nuclear weapon state, to whom it has given security assurances, is attacked by any other nuclear-weapon state. To sum up, the Court could not find any specific prohibition on using nuclear weapons under any treaty.

Public international law

As for the customary law, the Court stated that reliance be made to the Continental Shelf case, wherein it was noted that customary law should be ‘looked for primarily in the actual practice and opinio juris of states.’ States arguing for the prohibition of nuclear weapons on account of international customary law submitted that both the aforementioned requirements are being fulfilled. These states reached such a conclusion based on two grounds.

Firstly, many states submitted that since there has been no use of nuclear weapons since the end of WWII, it indicates the agreement of the international community not to use nuclear weapons. Thus, leading to a general conclusion that the use of nuclear weapons is prohibited. States not agreeing with the above-mentioned position responded that, at many times, states have reserved the right to use nuclear weapons in self-defense. In the words of the advisory opinion, ‘if nuclear weapons have not been used since 1945, it is not on account of an existing or nascent custom but merely because circumstances that might justify their use have not arisen.’ In the end, the Court sided with the latter view and concluded that opinio juris could not be deduced from mere lack of resorting to nuclear weapons by states. 

Besides that, some states also submitted that, for some decades, there had been a plethora of resolutions condemning the use of nuclear weapons. Reliance was heavily placed on UNGA Resolution 1653 (XVI), declaring the use of nuclear weapons contrary to the spirit of the UN Charter. However, since these resolutions have been passed without consensus, the Court noted that they could not amount to opinio juris.  


The Court’s ultimate conclusions on the question asked by the General Assembly came in six paragraphs, collectively regarded as operative provisions. Most of these paragraphs, as shown below, were mere reiterations of what the Court had already said. For instance, one such conclusion was that there is no specific authorization for the threat or use of nuclear weapons in both customary and international law. Besides that, the Court also declared that ‘a threat or use of force by means of nuclear weapons that is contrary to Article 2, paragraph 4, of the United Nations Charter and that fails to meet all the requirements of Article 51, is unlawful’ and the ‘threat or use of nuclear weapons should also be compatible with the requirements of the international law applicable in armed conflict.’ 

Lastly, the Court also urged states to pursue negotiations leading to nuclear disarmament as required under Article VI of the NPT. According to the then vice-president of the Court, these conclusions were ‘anodyne asservation[s] of the obvious.’ Such conclusions, therefore, seem as a concession to those asking for an express prohibition of the use of nuclear weapons and hardly justify the time taken by the Court to render its advisory opinion. 

It is, however, paragraph 105(2)(E) of the advisory opinion that warrants some analysis;

‘It follows from the above-mentioned requirements that the threat or use of nuclear weapons would generally be contrary to the rules of international law applicable in armed conflict, and in particular the principles and rules of humanitarian law;

However, in view of the current state of international law and of the elements of fact at disposal, the Court cannot conclude definitively whether the threat or use of nuclear weapons would be lawful or unlawful in an extreme circumstance of self-defence in which the very survival of a state is at stake.’

As for the first paragraph, it is unclear what the Court meant by the term ‘generally.’ However, the prima facie understanding of the paragraph leads us to conclude that there might be a scenario when the use of nuclear weapons would not violate the law of armed conflict. Nevertheless, it is unclear as to exactly what that scenario would be. One may argue that one such scenario could be the ‘use of low-yield nuclear weapons against warships’ as submitted by the US. Nevertheless, it cannot be concluded with certainty until a thorough examination of the nature of low-yield nuclear weapons.

Besides that, it must be noted that both paragraphs have brought two separate regimes, jus ad bellum, and jus in bello, in conflict with each other. It may be assumed, from the combined reading of paragraphs, that the use of nuclear weapons would generally be prohibited under IHL, but ‘an extreme circumstance of self- defense’ may permit its use. In other words, if a state’s own existence is in threat, it may use nuclear weapons and derogate from the norms of IHL. Such a starting point would surely be a blow to the progress already made in international law. 

Criticizing this reasoning of the majority,  Judge Higgins stated that ‘this goes beyond anything that was claimed by the nuclear weapons states appearing before the Court, who fully accepted that any lawful threat or use of nuclear weapons would have to comply with both the jus ad bellum and the jus in bello.’ In my opinion, this seems to be the incorrect application of the norms of international law, and had the Court stated that ‘the use of nuclear weapons would generally be contrary to the norms of international humanitarian law, but the states may use them if the requirement of the principle of proportionality has been met’ I believe that this reasoning of the Court would have been more consistent with what it had stated earlier. Besides that, it would have also avoided a conflict between jus ad bellum and jus in bello.


Under Article 38 of the Statute of the International Court of Justice, the Court must consider international conventions and customary law while giving an opinion on any question. In this opinion, the Court discussed nearly all the treaties relating to nuclear weapons, international human rights law, international humanitarian law, the UN Charter, and customary law. However, most conclusions the Court drew were either unwanted or just a mere concession to those who wanted an express prohibition on the threat and use of nuclear weapons. 

Firstly, even though the Court did state that the use of nuclear weapons is subject to the norms of IHL, it failed to appreciate the significance of both the principle of proportionality and the likelihood of widespread, long-term, and severe damage the use of nuclear weapons may cause to the environment. Secondly, the Court failed to comment regarding a scenario where nuclear weapons may be used in conformity with IHL. Lastly, as mentioned earlier, the prima facie understanding of the operative paragraph 105(2)(E) of the opinion suggests that a state may violate the principles of IHL when its existence is at stake. Such a starting point seems highly incompatible with the spirit of international law. The Court’s opinion may have upheld the principles of international law and seemed a step in the right direction, but this was not what the UNGA had wanted. 


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Ali Ahmed
Ali Ahmad is currently an Intern at Conflict Law Centre, RSIL. Previously, he did an Internship at Khatanas' Law Chamber and participated in 14th Henry Dunant Moot Court Competition. His main areas of interest include Public  International law, human rights law and International relations.