Israel – Hamas 2023 Symposium – White Phosphorus and International Law

Editor’s note: The authors’ original version of this post omitted citations to two sources, namely LTC Matthew J. Aiesi’s post on Lawfare dated November 26, 2019, and a Human Rights Watch report dated October 12, 2023. On 10 November, we corrected the post to include citations to each passage.

Human Rights Watch (HRW) has reported that the Israel Defense Forces (IDF) fired white phosphorus artillery rounds into southern Lebanon and Gaza City on October 10 and 11, respectively. Amnesty International’s Crisis Evidence Lab also released images of IDF troops in the town of Sderot alongside M109 155mm Howitzers and pallets of “M825 and M825A1 artillery shells, which are also labeled D528, the U.S. Department of Defense Identification Code for white phosphorus-based rounds.” Israel denies (here and here) that it has used white phosphorous in the ongoing conflict with Hamas, but various media outlets have published videos depicting what appears to be white phosphorous air-burst munitions in the sky over the port in Gaza City and in two rural locations along Israel’s border with Lebanon.

The HRW Middle East and North Africa director condemned Israel’s apparent use of white phosphorous on legal grounds and claimed that “[t]he use of white phosphorus in Gaza . . . violates the international humanitarian law prohibition on putting civilians at unnecessary risk.” The full HRW report concludes that white phosphorous “can be used as an incendiary weapon” and that its use “in densely populated areas of Gaza violates the requirement under international humanitarian law to take all feasible precautions to avoid civilian injury and loss of life.” Amnesty International also opined that the IDF’s use of white phosphorus in densely populated civilian areas in Gaza may be considered “unlawful indiscriminate attacks.”

In this post, we describe white phosphorus and discuss why and how militaries use it. We then consider whether white phosphorous munitions are illegal per se or violate treaties addressing the use of incendiary and chemical weapons. Finally, we turn to the law of armed conflict rules applicable to the use of all munitions, including white phosphorus weapons. Our conclusion is that, as always, the application of the law of armed conflict is contextual. Whether the use of white phosphorous violates the law depends on the circumstances and manner of its use, which, in the present case, remain unclear.

White Phosphorus on the Battlefield

White phosphorous, or tetraphosphorus, has been defined as “a toxic, colorless, white or yellow waxy solid with a garlic-like odor. It does not occur naturally and is manufactured from phosphate rocks. White phosphorus ignites when it reacts with oxygen, producing thick clouds of white smoke and reaching temperatures high enough to burn through metal.” White phosphorous munitions spread burning phosphorous at extreme temperatures. It continues to burn until completely “depleted” or no longer exposed to oxygen.

Militaries employ various types of white phosphorous munitions, primarily for marking and illuminating targets and to create smokescreens to protect maneuvering friendly forces. When used to create smoke or to illuminate targets at night, the risk to personnel is minimal. White phosphorous may also be used as an anti-personnel weapon under some circumstances and can be delivered by artillery (land and naval). Because of its favorable smoke-to-weight ratio, it can even be delivered by mortar or hand grenade. As Ian MacLeod and Anthony Rogers have explained,

The armed forces have a legitimate requirement for substances that can be used to illuminate a battlefield at night or to provide cover during daylight, to mark a target, to assist in range-finding or to set fire to material targets such as ammunition or fuel stores. [White phosphorus] is suitable for many of these tasks because it ignites easily when exposed to oxygen and produces dense white smoke. Ideal for laying a quick smoke screen, it can also be used as a component of incendiary weapons, or of tracer, or to indicate a target or illuminate enemy positions.

The use of white phosphorous is not new. For instance, the American and British armies employed it throughout the Second World War for the purposes described above. The British Special Air Services used white phosphorous grenades in the Falklands to flush enemies out of their fighting positions. In 2004, the United States military used white phosphorous during the second battle of Fallujah to “smoke out” concealed fighters and attack them. More recently, U.S. forces used it in battles with the Islamic State to screen and obscure friendly forces and to mark and illuminate enemy targets.

In late 2008 and early 2009, Israel fired white phosphorus munitions into Gaza for the purposes of marking, signaling, and screening. The Israeli Ministry of Foreign Affairs (MFA) stressed that “no exploding munitions containing white phosphorous were used in built-up areas of the Gaza Strip or for anti-personnel purposes.” The MFA also explained that the white phosphorous munitions “may, on occasion, produce incidental incendiary effects, but this does not make them incendiary weapons for purposes of international law” (para. 407).

The Law

There is no per se prohibition on the use of white phosphorous. For instance, a March 2009 HRW report notes that “[w]hen used properly in open areas, white phosphorous munitions are not illegal.” A 2017 article in the New York Times likewise noted that “it is not illegal under international law for militaries to possess and use white phosphorus.” The military manuals of several States indicate that it may be used lawfully, even as an anti-personnel weapon, in certain circumstances (e.g., United States (§ 6.14.2.1), Canada (para. 521.3.), France (p. 20-21), Germany (paras. 453-458), and Australia (paras. 4.30-31)). The question, then, is whether the use of white phosphorous munitions is restricted by weapons treaty law or the law of armed conflict rules governing the conduct of hostilities.

Treaty Law

White phosphorus munitions are often characterized as “incendiary weapons” or “chemical weapons.” In this regard, many commentators point to the Protocol on Prohibitions or Restrictions on the Use of Incendiary Weapons (Protocol III) to the 1980 Convention on Certain Conventional Weapons and/or the Convention on the Prohibition of the Development, Production, Stockpiling and Use of Chemical Weapons and on their Destruction (CWC) when analyzing the use of white phosphorus munitions in armed conflict. Both treaties apply in international and non-international armed conflicts (Protocol III, amendment to art. 1; CWC, art. 1(1)).

White phosphorus munitions are not considered an “incendiary weapon,” as that term appears in Protocol III. Article 1 of Protocol III defines an “incendiary weapon” as “any weapon or munition which is primarily designed to set fire to objects or to cause burn injury to persons through the action of flame, heat, or combination thereof, produced by a chemical reaction of a substance delivered on the target.” In fact, Article 1(b)(i) excludes from the definition munitions “which may have incidental incendiary effects, such as illuminants, tracers, smoke or signalling [sic] systems.”

According to the U.S. Department of Defense Law of War Manual, “white phosphorous is a munition … [that] is intended primarily for marking or illuminating a target or masking friendly force movement by creating smoke” (§ 6.14.1.3). Because white phosphorus munitions are primarily designed for marking, screening, illuminating, and signaling, their burning effects are incidental. As a result, Protocol III does not apply.

But even if white phosphorous munitions did qualify as “incendiary weapons,” Protocol III would not ban their use. Rather, it regulates the use of incendiary weapons by parties to the instrument for the purpose of protecting civilians.

Article 2 of the instrument sets forth the restrictions:

1. It is prohibited in all circumstances to make the civilian population as such, individual   civilians or civilian objects the object of attack by incendiary weapons.

2. It is prohibited in all circumstances to make any military objective located within a concentration of civilians the object of attack by air-delivered incendiary weapons.

3. It is further prohibited to make any military objective located within a concentration of civilians the object of attack by means of incendiary weapons other than air-delivered incendiary weapons, except when such military objective is clearly separated from the concentration of civilians and all feasible precautions are taken with a view to limiting the incendiary effects to the military objective and to avoiding, and in any event to minimizing, incidental loss of civilian life, injury to civilians and damage to civilian objects.

4. It is prohibited to make forests or other kinds of plant cover the object of attack by incendiary weapons except when such natural elements are used to cover, conceal or camouflage combatants or other military objectives, or are themselves military objectives.

In sum, Article 2 of Protocol III regulates the circumstances under which the weapons can be used, to mitigate collateral effects on civilians.

Note that Israel is not a party to Protocol III and is therefore not formally bound by its terms. And the detailed rules in Articles 2(2) to 2(4) do not reflect customary international law International Committee of the Red Cross (ICRC) Customary International Humanitarian Law study, rule 84). However, in practice, Israel generally applies Protocol III’s principles. Additionally, as HRW noted,

In 2013, in response to a petition to Israel’s High Court of Justice regarding the use of white phosphorus in Gaza, the Israeli military stated that it would no longer use white phosphorus in populated areas except in two narrow situations that it revealed only to the justices. In the court’s ruling, Justice Edna Arbel said that the conditions would “render use of white phosphorous an extreme exception in highly particular circumstances.

The United States is a party to Protocol III, but it has issued a reservation regarding both Article 2(2) and 2(3). Specifically, the United States,

reserves the right to use incendiary weapons against military objectives located in concentrations of civilians where it is judged that such use would cause fewer casualties and/or less collateral damage than alternative weapons, but in so doing will take all feasible  precautions with a view to limiting the incendiary effects to the military objective and to  avoiding, and in any event to minimizing, incidental loss of civilian life, injury to civilians and  damage to civilian objects.

It is also sometimes asserted that white phosphorous is a chemical weapon, the use of which is banned by the CWC. Article 2 of the CWC defines “chemical weapons” as:

(a) Toxic chemicals and their precursors, except where intended for purposes not prohibited under this Convention, as long as the types and quantities are consistent with such purposes;

(b) Munitions and devices, specifically designed to cause death or other harm through the toxic properties of those toxic chemicals specified in subparagraph (a), which would be released as a result of the employment of such munitions and devices;

(c) Any equipment specifically designed for use directly in connection with the employment        of munitions and devices specified in subparagraph (b).

As with Protocol III, white phosphorous falls outside of the CWC’s purview because it is not “specifically designed to cause death or other harm” by means of a “toxic chemical.” A “toxic chemical” is defined as “[a]ny chemical which through its chemical action on life processes can cause death, temporary incapacitation or permanent harm to humans or animals” (emphasis added). Even though white phosphorous produces incredible temperatures through a chemical process, it does not, by “chemical action on life processes” cause death or temporary incapacitation. In addition, white phosphorus munitions are specifically designed for illumination, marking, signaling, and screening; not for causing death or other harm. As a result, white phosphorus munitions do not fall within the CWC’s definition of a chemical weapon. As Matthew Aiesi noted in 2019, the CWC annexes incorporate a list of known toxic chemicals and their precursors. Tetraphosphorus is not listed.

In conclusion, neither Protocol III nor the CWC bans white phosphorus munitions. White phosphorus does not meet the definition of an “incendiary weapon” under Protocol III. And, even if it did, Israel is not a party to the Protocol nor are the treaty’s restrictions customary in character. Similarly, white phosphorus does not fall within the CWC’s definition of a “chemical weapon.”

Conduct of Hostilities Rules

Although not subject to the aforementioned treaties, the use of white phosphorous is always governed by the law of armed conflict’s conduct of hostilities rules. As Peter Herby, then the head of the ICRC’s Arms Unit observed in 2009:

The use of weapons containing white phosphorous is, like the use of any other weapon, regulated by the basic rules of international humanitarian law. These require parties to a conflict to discriminate between military objectives on the one hand and civilians and civilian objects on the other. The law also requires that they take all feasible precautions to prevent harm to civilians and civilian objects that can result from military operations. Attacks which cause “disproportionate” damage to civilians and to civilian objects are prohibited.

His comments make clear, correctly in our view, that each use of white phosphorus must be evaluated under law of armed conflict rules, specifically, distinction (discrimination), proportionality, unnecessary suffering, and feasible precautions.

Indiscriminate attacks are, in part, those “which are not directed at a specific military objective.” (ICRC, Customary International Humanitarian Law study, rule 12). An armed force may not fire white phosphorus munitions at civilians or civilian objects, nor use the munitions without aiming them (e.g., by firing them into an area in which there are separated civilian objects and military objectives without aiming at the latter).

The rule of proportionality prohibits an attack expected to cause harm to civilians or civilian objects that would be excessive in relation to the concrete and direct military advantage anticipated (ICRC, Customary International Humanitarian Law study, rule 14). Thus, the military advantage an attacker hopes to gain by using white phosphorous munitions (e.g., illumination of an enemy target at night; screening troop movements, etc.) must be assessed against the collateral damage to civilians and civilian objects likely to be caused by the burning phosphorus embers.

The principle of unnecessary suffering (or humanity) focuses on the effects a weapon system has on combatants (ICRC, Customary International Humanitarian Law study, rule 70). While the principle of unnecessary suffering is widely accepted, the exact meaning and regulatory implementation varies between States (see Professor Sean Watts’s previous Articles of War post for an in-depth discussion). While some States apply the standard set forth in Article 35(2) of Additional Protocol I to the 1949 Geneva Conventions (AP I), Israel and the United States (neither is a party to AP I) apply the standard set forth in Article 23(e) of the Regulations annexed to the 1907 Hague Convention IV (Hague IV), which states “it is especially forbidden . . . [t]o employ arms . . . calculated to cause unnecessary suffering” (emphasis added) (see DoD Law of War Manual, § 6.6.1. and Israel’s Statement on Lethal Autonomous Weapons Systems (LAWS) Weapon Legal Review).

As discussed, white phosphorus munitions are primarily designed and used for illumination, marking, signaling, and screening. They are not unlawful per se because they are designed to achieve a specific military advantage (DoD Law of War Manual, § 6.14.1.3; The Operation in Gaza 27 December 2008 – 18 January 2009 – Factual and Legal Aspects, para. 405). Even used as an anti-personnel weapon, white phosphorus munitions are lawful so long as the suffering imposed by their use is necessary to accomplish a legitimate military purpose (DoD Law of War Manual, § 6.14.2.1).

Finally, combatants are required to take “feasible precautions” to avoid or minimize “incidental loss of civilian life, injury to civilians and damage to civilian objects” (ICRC, Customary International Humanitarian Law study, rule 15). Feasible precautions include, for example, the use of different munitions (if available), warnings to civilians, deciding to use the munitions only in rural areas, and weaponeering, such as changing the direction and altitude of the air-burst to decrease the potential for collateral damage.

The application of the law of armed conflict to the use of white phosphorus munitions must be done on a case-by-case basis. Like the use of any munition in combat, whether the use of white phosphorous munitions is lawful depends on the attendant circumstances.

Concluding Thoughts

The use of white phosphorus munitions, even in an urban environment, would not violate international law per se. Instead, because there is no weapons control treaty that prohibits their use altogether, any use of the munitions would have to be evaluated against the law of armed conflict’s conduct of hostilities rules. In this case, Israel has denied reports that the IDF used white phosphorus munitions in Gaza. However, even if they had been used, the lawfulness of their use would depend on the facts and surrounding circumstances, as is the case with all attacks.

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Major Kevin S. Coble is an active-duty Army judge advocate and a military professor in the Stockton Center for International Law in Newport, Rhode Island.

Major John C. Tramazzo is an active-duty Army judge advocate and a military professor in the Stockton Center for International Law in Newport, Rhode Island.

Photo credit: National Archives and Records Administration