[Just Security is publishing a series of articles by legal experts discussing the major UN report on the Yemen War. This is the first article in the series. Stay tuned for the next article in the series by Professor Adil Haque.]

Last week, the Report of the Group of Eminent International and Regional Experts on Yemen (Expert Report) was released by the UN Human Rights Council. It found an array of human rights and international humanitarian law (IHL) violations in the non-international armed conflict underway since late 2014, some of which the Expert Report characterizes as war crimes. As summarized by the Experts,

Shelling and airstrikes create the sense that there is no safe place to hide from the fighting.  Landmines left by the Houthis kill and maim people long after battles have subsided. The blockade, siege-like tactics, attacks impacting objects essential to the survival of the population and impediments to the delivery of aid deprive the population of necessary items amidst the unprecedented humanitarian crisis.  People are arrested and detained arbitrarily, disappeared, and subjected to torture and ill-treatment, including sexual violence. The population lives in fear of being detained or otherwise targeted for any perceived dissent.

The assessment that the “impact of these violations on the lives of ordinary Yemenis … has been immense and wide ranging” cannot be disputed. In reaching their final conclusions, the Experts applied IHL, including certain interpretations of IHL rules that remain contested among States, to complex conditions of urban warfare. In this post, we focus in on the “siege-like tactics” cited in the Expert Report and explain how the IHL rules on starvation, proportionality, and precautions in attacks applied to the Siege of Ta’izz.

The Siege of Ta’izz

In 2015-2016, a battle for the city of Ta’izz was fought between the Houthi-Saleh fighters and Yemeni armed forces loyal to President Hadi that were operating together with various loosely organized armed groups (supported by the Saudi-led Coalition). During the battle, the Houthi-Saleh fighters cut the two main supply roads into the city after having been pushed to its outskirts. The UN Humanitarian Coordinator for Yemen described Ta’izz as “under a virtual state of siege” in which “[l]ittle, if any, commercial goods or humanitarian assistance have been able to enter the [affected] districts.” Houthi restrictions on transportation into the besieged areas of the city included such essential civilian goods as medical supplies and equipment, gas cylinders for cooking, and food other than small amounts for personal consumption; in some cases, medical and humanitarian personnel were barred from entering the city. Among the tactics employed to enforce the siege was the use of snipers to shoot civilians at checkpoints. The Houthi forces allowed civilians to leave the city and, reflective of the harsh conditions resulting from the conflict and ensuing siege, by October 2015 only 175-200,000 civilians remained, roughly one-third of the original population.

In March 2016, Yemeni armed forces opened one of the roads into the city, thereby breaking the siege, but access was still very limited, delivery of humanitarian assistance continued to be severely hampered, and the humanitarian situation remained dire. In a sense, the siege continued, albeit not at the previous level. Other areas of the country have also been subjected to siege-like restrictions, including on humanitarian assistance, that have caused severe civilian suffering.

Sieges and International Humanitarian Law

Siege as a method of war was mentioned as far back as the writings and iconography of Israel, Mesopotamia and early Persia. Despite its long lineage, the term “siege” is nowhere authoritatively defined in international law. Nevertheless, the Expert Report accurately captures the prevailing appreciation of the tactic as “military encirclement of an area with the imposition of restrictions on the entry and exit of essential goods with the aim of forcing its surrender.”

Both Article 27 of the 1907 Hague Regulations and Article 17 of the 1949 Fourth Geneva Convention implicitly treat sieges as a lawful method of warfare, while the U.S. Department of Defense (DOD) Law of War Manual (DOD Manual) provides that “it is lawful to besiege enemy forces, i.e., to encircle them with a view towards inducing their surrender by cutting them off from reinforcements, supplies, and communications with the outside world.” The Expert Report is in accord, for it observes that “[b]lockades, sieges and siege-like warfare are not per se prohibited by international humanitarian law, as long as their purpose is to achieve a military objective and they are not imposed with the purpose to starve the civilian population.”

Sieges and Starvation of the Civilian Population

As Yoram Dinstein has observed, the “essence of siege warfare lies in an attempt to capture the invested location through starvation.” Indeed, recognizing that “[w]ar is not carried on by arms alone,” the Civil War-era Lieber Code provided that “[i]t is lawful to starve the hostile belligerent, armed or unarmed, so that it leads to the speedier subjugation of the enemy.”

Of course, IHL has progressed significantly since the Lieber Code. In modern warfare, it is unquestionable that IHL prohibits intentional starvation of the civilian population. In treaty law, the prohibition is found in Article 54(1) of Additional Protocol I to the 1949 Geneva Conventions for international armed conflict and Article 14 of Additional Protocol II (AP II) for non-international armed conflicts, such as that in Yemen. Yemen is a Party to that conflict, which clearly reaches AP II’s  Article 1 threshold of applicability because Houthi forces control significant swaths of territory. There is also general consensus that the prohibition on starving the civilian population as a method of warfare is customary in character vis-a-vis both international and non-international armed conflict, as is attacking, destroying, removing or rendering useless objects indispensable to the civilian population (such as food and water) for the purpose of denying their sustenance value to the civilian population.

From a practical perspective, the commander of a besieging force will generally want civilians to leave the besieged area since this will ease legal constraints on attacks. For example, if civilians are absent, it will be more straightforward to apply the rule of proportionality (which provides that expected incidental harm to civilians and civilian objects must not be excessive in relation to the anticipated military advantage of an attack) and the requirement to take precautions in attack to minimize harm to civilians, including attacks against food stores and other essential items that may enhance the siege’s effects. Civilians could, however, choose to stay put, as a portion of the population has done in Ta’izz, perhaps for fear of an even more uncertain fate if they leave. They might also be unlawfully compelled to remain in a besieged area to complicate the besieging force’s attacks. In such cases, the question is how the impact of the siege on the civilian population affects its lawfulness.

Proportionality and Precautions during Sieges

The Expert Report takes the position that the impact of a siege on the civilian population is subject to the rule of proportionality. In adopting the same position, the DOD Manual provides, “Military action intended to starve enemy forces, however, must not be taken where it is expected to result in incidental harm to the civilian population that is excessive in relation to the military advantage anticipated to be gained.” Of course, the practical concern for a commander lies in gauging how long an adversary will hold out prior to surrender and assessing the degree of civilian harm likely to occur in the meantime; but that is a practical, not legal obstacle.

Additionally, the DOD Manual applies the customary law requirement to take precautions in attack to minimize harm to civilians during siege warfare intended to starve the enemy: “Feasible precautions to reduce the risk of harm to the civilian population or other reasonable measures to mitigate the burden to the civilian population may also be warranted when seeking to starve enemy forces.” Such precautions would include cancelling or suspending the siege if it becomes apparent that incidental loss of civilian life is greater than originally expected and is likely to now be excessive in relation to the anticipated military advantage. Warning the civilian population of the imposition of the siege in order to allow it to flee would likewise qualify as a precautionary measure.

The application of the requirement to take precautions in attack is of particular importance. It was long the case that a besieging force could prevent the departure of the civilian population in order to exacerbate the lack of food, water, and other supplies for their besieged opponents and thereby hasten their surrender. Both the DOD Manual and the U.S. Army and Marine Corps’ newly published Commander’s Handbook on the Law of Land Warfare (Field Manual 6-27) rightly conclude that using force to push civilians back into the besieged locality is now unlawful, citing inconsistency with the duty to take feasible precautions.

An Obligation to Allow Delivery of Humanitarian Assistance?

In order to comply with the rule of proportionality and the requirement to take feasible precautions to minimize civilian harm, a besieging party may allow the delivery of humanitarian assistance, which could make compliance with those rules possible while maintaining the siege. However, this leaves open the question of whether a besieging force is obligated to permit delivery of such assistance when the actual or expected civilian harm is not presently excessive relative to the anticipated military advantage of the siege. Along similar lines, when is the delivery of humanitarian assistance not “feasible” because it might be diverted to use by the enemy forces and thereby diminish the military effectiveness of the siege?

The Expert Report asserts that during a siege “the parties to the conflict must allow and facilitate rapid and unimpeded passage of humanitarian relief for civilians in need, which is impartial in character and conducted without any adverse distinction, and subject to their right of control.” This approach follows that of other commentators on the subject (see, e.g., Akande/Gillard, Blank and Van Schaack). In a non-international armed conflict like that in Yemen, this purportedly customary rule is captured for Parties to AP II in Article 18, which applies when “the civilian population is suffering undue hardship owing to the lack of supplies essential for its survival.” Recall that Yemen is a Party to AP II and thus both government and insurgent forces are bound by its terms.

Article 18 of AP II also states, however, that relief actions shall be undertaken with the consent of the High Contracting Party. We concur with the Oxford Guidance on the Law Relating to Humanitarian Relief Operations in Situations of Armed Conflict, which notes that although parties are entitled to prescribe technical arrangements for passage, “such measures must be applied in good faithand their nature, extent, and impact must not prevent the rapid delivery of food assistance in a principled manner.” In particular, and as noted in the ICRC Commentary to Article 18, consent “does not mean that the decision is left to the discretion of the parties.”

Thus, without reasonable grounds, the parties to an international or non-international armed conflict cannot refuse or otherwise impede such relief. As noted in the Expert Report, “[c]onsent may not be withheld for arbitrary reasons, and restrictions on humanitarian activities may only be justified in case of imperative military necessity and on a temporary basis.” In our view, such necessity presents itself during a siege if the supplies concerned are being, or there are reasonable grounds to believe they will be, diverted for use by the besieged force. However, the siege must be lifted if that diversion gives rise to excessive civilian harm (the proportionality rule).

As noted in the Expert Report, these rules are “subject to debate among scholars and practitioners.” A prominent example is found in the UK Manual on the Law of Armed Conflict (UK Manual), which provides “so long as the besieging commander left open his offer to allow civilians and the wounded and sick to leave the besieged area, he would be justified in preventing any supplies from reaching that area.”  The UK Manual, therefore, appears to conclude that incidental starvation of civilians is permitted where a siege is being conducted and all practicable steps have been taken by the besieging commander to allow civilians and fighters rendered hors de combat to leave the area in advance of or during an ongoing siege.

The DOD Manual is more nuanced.  In the specific context of siege warfare, it adopts the 1949 Geneva Convention IV, Article 23, requirement that the following items are entitled to free passage if they will be used solely by the civilian population: “medical and hospital stores and objects necessary for religious worship intended only for civilians; and all consignments of essential foodstuffs, clothing, and tonics (i.e., medicine) intended for children under fifteen, expectant mothers, and maternity cases.” It acknowledges no further obligation to allow passage of any supplies. Additionally, while the DOD Manual encourages the execution of agreements on the matter, it expressly rejects any categorical legal obligation to permit the “removal of wounded, sick, infirm and aged persons, children, and maternity cases, or … the passage of ministers of all religions, medical personnel, and medical equipment on their way to such areas.” Nevertheless, the DOD’s adoption of the requirement of precautions in attack would suggest that other relief supplies must be allowed in unless they enhance the enemy’s ability to withstand the siege, while its application of the rule of proportionality means that a siege must be lifted if expected harm to civilians is excessive relative to the anticipated military advantage of the siege, i.e., the surrender of enemy forces.

Some commentators have likewise questioned a general obligation to allow humanitarian relief during a siege. While conceding that modern IHL requires parties to the conflict to afford civilians the opportunity to leave the besieged area, Yoram Dinstein asks,

… if civilians in a besieged venue are offered a safe passage out of an encircled area but choose to stay in situ, what lawful claim do they have for special protection from the hardships of starvation?  In a similar vein, if the civilians are coerced to stay where they are by edict of the military commander of the besieged force, why should the enemy be barred from … sealing hermetically an enveloped space[?].

He is not alone. Sean Watts has suggested,

With respect to siege operations, no military consideration is clearer than the absolute imperative of imposing complete physical, psychological, and electronic isolation.  What may appear to some as inadequacies of the law regulating relief actions, including discretion to reject offers of impartial humanitarian relief, may actually be reflections of States’ armed forces’ considerable military experience with siege.  Discretion to withhold consent to offers of humanitarian relief actions is an entirely logical, if potentially cruel, outgrowth of the isolation imperative and operational experience.

Concluding Thoughts

Sieges are lawful so long as directed at enemy forces (and not intended to starve the civilian population), compliant with the rule of proportionality, and consistent with the requirement to take precautions in attack. As to the obligation to allow humanitarian assistance, we realize that the views expressed in the US and UK manuals and by the aforementioned scholars reflect the traditional understanding of siege law. We also understand that one must be cautious in interpretive ventures, especially given the military and humanitarian stakes at risk with respect to IHL rules. Yet, interpretation of such rules necessarily evolves over time to reflect the international community’s balancing of military necessity and humanitarian considerations, as is illustrated in the DOD Manual’s acknowledgement that it is no longer lawful to use force to keep civilians in a besieged area.  Accordingly, we are at ease endorsing the Expert Report’s conclusions on the state of the law, subject to the important condition that a besieged force not use humanitarian relief supplies for its own purposes.

Our only hesitancy comes, therefore, with respect to the Expert Report’s finding of a breach of the obligation to allow humanitarian supplies into the besieged areas. The Experts note that aid was sometimes diverted for use by the besieged forces. However, there is no indication as to the besieging forces’ rationale for blocking delivery. If delivery of the essential supplies for the civilian population were blocked based on a reasonable belief that they would be used by the besieged forces, our view is that there was no violation of IHL – unless the siege caused excessive harm to the civilian population, thus running afoul of the rule of proportionality. Yet, if the motivation was for any other purposes, such as maliciousness or to seize them for the besieging force’s own use, blocking or otherwise hindering delivery was unlawful regardless of whether proportionality was also violated. Finally, we note that it appears from the reports of civilian suffering that the siege of Ta’izz violated the rule of proportionality and the requirement to take precautions in attack. However, without greater granularity on the military advantage the siege afforded Houthi forces, any definitive conclusion along these lines would be somewhat premature.


IMAGE: Yemeni fighters loyal to the country’s exiled President Abedrabbo Mansour Hadi ride a tank past a destroyed building during clashes with Shiite Huthi rebels in the country’s third-city of Taez on May 30, 2019. – Taez, in southern Yemen, is under siege by the Huthis but controlled by pro-government forces, who are supported by the military coalition led by Saudi Arabia and the United Arab Emirates. (Photo by AHMAD AL-BASHA/AFP/Getty Images)