The Anti-ISIL Coalition, Civilian Harm, and the Obligation to Investigate

by | Aug 30, 2023


This post is drawn from the author’s article-length work, “How Does the Obligation to Investigate Alleged Serious Violations of International Humanitarian Law Apply in Ad Hoc Military Coalitions?” appearing in The Military Law and the Law of War Review.

In recent years, investigative journalists and non-governmental organisations have repeatedly alleged that several States, including the United States, United Kingdom, Denmark, and the Netherlands caused significant civilian casualties during Operation Inherent Resolve, the U.S.-led military coalition established in 2014 to defeat the Islamic State of Iraq and the Levant (ISIL). Most recently, investigative journalists claimed that UK airstrikes caused the deaths of multiple civilians during the Battle of Mosul in 2016-2017, despite previous claims by the British Government that its entire air campaign against ISIL had caused no civilian deaths. A consistent theme regarding the alleged civilian deaths—currently estimated by Airwars, a UK-based non-profit, to number between 8,198 and 13,258—is the lack of clarity regarding which State(s) carried out individual airstrikes and whether the States concerned adequately investigated afterwards.

In light of these allegations of civilian harm, this post examines how the obligation to investigate alleged violations of international humanitarian law (IHL) applies to States involved in military coalitions such as Operation Inherent Resolve. It concludes that States involved in military coalitions must proactively cooperate with one another to fulfil their respective obligations to investigate alleged violations of IHL.

Operation Inherent Resolve

“Combined Joint Task Force – Operation Inherent Resolve,” the military component of the wider “Global Coalition against Daesh,” was established on 15 October 2014 with the aim of “eliminat[ing] the terrorist group ISIL and the threat they pose to Iraq, the region and the wider international community.” Several States, however, had already started targeting ISIL with airstrikes by at least August 2014 in response to the group’s swift territorial gains throughout the region.

The States involved in Operation Inherent Resolve contributed in various ways, including through direct military engagement against ISIL, reconnaissance, and air-to-air refuelling (p. 8-11). Direct military action mainly consisted of the use of artillery and airstrikes—involving piloted aeroplanes and drones—against identified ISIL targets and in support of allied ground troops, such as the Iraqi security forces. Some States, most notably the United States, also provided ground troops, including special forces, to support and advise. In total, at least 29 States were actively involved in Operation Inherent Resolve (p. 1), with at least 14 taking a direct kinetic role. Owing to the political context and the related international legal issues—namely, that Syria did not openly consent to Operation Inherent Resolve targeting ISIL within its territory (e.g., see here)—several States restricted their engagements against ISIL to within Iraq.

Although Operation Inherent Resolve remains functional, with the aim of “advis[ing], assist[ing] and enable[ing] partnered forces until they can independently defeat Daesh [ISIL] in designated areas of Iraq and Syria . . . ,” the coalition was most active between 2014 and the fall of ISIL’s last territorial stronghold in the region in March 2019. As such, this post focuses on this period.

Structure of the Coalition

Unlike more formalised military coalitions such as the North Atlantic Treaty Organisation (NATO), Operation Inherent Resolve does not constitute an international organisation. Instead, Combined Joint Task Force – Operation Inherent Resolve was created under the overall coordination of U.S. Central Command (CENTCOM). Coalition airstrikes were planned and coordinated from the Combined Air Operations Center located at the United States’ al-Udeid Air Base in Qatar, and coalition members’ aircraft operated from several bases in the surrounding region, including in Qatar, Cyprus, Turkey, and the United Arab Emirates (p. 10-12).

Although coming under the United States’ overall command, each contributing State within Operation Inherent Resolve retained its own rules of engagement (RoE): directives that define “the conditions and manner in which the use of force may be applied” (p. 10). These RoE include “caveats” which allow each State to opt-out of a specific attack if it might conflict with their IHL obligations, legal interpretations, and/or political imperatives. Central to the caveat system is the role of “Red Card Holder Teams” sent from each coalition State (p. 350). These teams, which include national military legal experts, must consent to each request for their respective military to engage a target. Therefore, although multiple States were regularly involved in the targeting process during Operation Inherent Resolve (p. 12-17), the State whose military carried out the attack—e.g., the aircraft that engaged the target—retained the opportunity to refuse.

Civilian Harm Allegations

Operation Inherent Resolve’s role in helping to reverse ISIL’s territorial gains and thus ending their abhorrent acts, many of which amounted to international crimes, should not be overlooked. Nevertheless, despite being portrayed as a meticulous, precision-based campaign, it is alleged that many thousands of civilians were killed and injured. Allegations of civilian harm incidents, largely collated through victim testimony and open source research, can be found on databases created by Airwars and Amnesty International, among others. One prominent example is the June 2015 airstrike carried out by Dutch F-16s on an improvised explosive vehicle factory in the ISIL-controlled city of Hawija, Iraq, that is estimated to have caused at least 85 civilians deaths, largely as a result of secondary explosions. Members of the coalition established a “Civilian Casualty Cell” in December 2016 to assess and track allegations of civilian harm such as these (p. 19-21). The Cell has faced criticism, however, for insufficient funding and staffing, as well as making findings at odds with credible evidence.

It must be emphasised that not every death or injury caused during an armed conflict constitutes a violation of IHL. Indeed, under customary targeting law, incidental civilian harm is permissible when the expected civilian harm is not excessive “in relation to the concrete and direct military advantage anticipated” (International Committee of the Red Cross (ICRC), Rule 14; Additional Protocol I, art. 51(5)(b)). There were, however, several instances during Operation Inherent Resolve when it is alleged that either all feasible precautions in attack were not taken as required by IHL, and/or attacks were disproportionate because the expected civilian harm was excessive in relation to the “concrete and direct” military advantage anticipated. In such situations, the obligation to investigate, as described below, was likely triggered.

Notably, with the exception of several airstrikes in 2014, the State(s) that carried out individual attacks within Operation Inherent Resolve were not publicly named. According to some reports, the decision to anonymise attacks stemmed from fear among coalition members that ISIL or ISIL-affiliated actors would retaliate via mass-casualty terrorist attacks, which were a significant threat during that period. Others suggest that coalition partners preferred anonymity to prevent civilian harm being attributed to them (p. 21-22). Regardless, the involvement of several States in an attack that appears to violate IHL, even in situations where States’ roles are not (publicly) known, does not negate each State’s obligation to investigate.

The Obligation to Investigate

There are little to no provisions within the Geneva Conventions or their Additional Protocols that explicitly mention the obligation to investigate, indicate when it is triggered, or describe what is required. Instead, the obligation is drawn from various provisions within IHL treaty law, most notably the grave breaches regime and Common Article 1 (the duty to respect and to ensure respect for IHL), customary international law, and international human rights law (for a useful summary, see here).

The grave breaches provisions require States to criminalise and prosecute serious IHL violations committed by their troops and/or within their jurisdiction, including through “search[ing] for . . . and bring[ing] such persons . . . before its own courts” (e.g., GC I, art. 49). Although these provisions only apply to an exhaustive list of serious violations of IHL committed in international armed conflicts, the ICRC’s Customary IHL Study asserts that the obligation to investigate war crimes applies to all serious violations of IHL, including in non-international armed conflicts (NIACs) (Rule 158). Most commentators and courts have accepted this as accurately reflecting customary IHL (e.g., here and here, paras. 82-83).

In addition, States must “suppress” all other non-serious violations of IHL. This duty to suppress is also considered to give rise to an obligation to investigate (p. 42-43). Furthermore, if the ICRC and several scholars’  interpretation of the external duty to ensure respect for IHL is embraced (as I do here, p. 210-212), this requires States, particularly those in close proximity, to assist one another to fulfil their obligation(s) to investigate (GCs, art. 1; ICRC, Rule 144).

The second report of the Turkel Commission, established by the Israeli Government in 2010, specifies that the obligation to investigate is triggered “where a credible accusation is made or a reasonable suspicion arises that a war crime has been committed” (p. 100), a standard widely accepted in the literature (here, p. 52, and here, p. 207). In relation to an investigation’s requirements, the 2019 ICRC/Geneva Academy Guidelines on Investigating Violations of International Humanitarian Law states that investigations should be “capable of [1] enabling a determination of whether there was a violation of international humanitarian law, [2] identifying the individual and systemic factors that caused or contributed to an incident, and [3] laying the ground for any remedial action that may be required” (p. 9). Although the extent to which these standards reflect customary international law is unclear, they provide a useful reference point.

The Obligation to Investigate and Operation Inherent Resolve

Perhaps predictably, the obligation to investigate becomes more complex when multiple States contribute to the targeting cycle, civilian harm is suffered, and violations of IHL are alleged. As I argued in a recent journal article, however, the obligation to investigate continues to apply during military cooperation. Furthermore, it can be triggered even when a State’s military is not directly involved in the underlying IHL violation, and military coalition members must collaborate to establish the circumstances surrounding the alleged violation.

In the context of Operation Inherent Resolve, it can firstly be presumed—owing to the large number of engagements between coalition members and ISIL, as well as ISIL’s high level of organisation—that a NIAC existed between the militarily active coalition member States and ISIL, at least between 2014 and 2019. As the obligation to investigate IHL violations presumes the existence of an armed conflict, this is a necessary consideration.

In situations when a credible accusation or reasonable suspicion of a (serious) violation of IHL arose following, for example, an airstrike carried out by State A, based on intelligence from State B, and initiated by State C, the obligation to investigate is triggered at several stages. First, the customary obligation to investigate requires all States involved in the attack to investigate the role of their military in the targeting process. This primary obligation applies to each State until the identity of the responsible individual(s) is determined. Once established, the State of nationality (e.g., the State in whose military the individual belongs) will, owing to their jurisdiction, have the primary obligation to investigate and, if necessary, prosecute that individual. However, all States involved, in line with their external obligation to ensure respect for IHL (GCs, Common Article 1; see also ICRC, Rule 161), are required to take feasible steps to assist in the investigation. This due diligence obligation will be more onerous for the States closely involved in the attack, as well as those that hold relevant information or evidence.

While States involved in Operation Inherent Resolve can fulfil their obligation to investigate through supporting the Civilian Casualty Cell, its existence does not automatically satisfy those States’ obligations to investigate. In other words, States cannot unconditionally surrender their investigative responsibilities to a centralised body. Instead, they must ensure that any such entity fulfils the States’ own substantive obligations. If it does not, the States in question will violate their respective obligations to investigate.

Although a simple example, it is clear that cooperation is an essential requirement for the satisfaction of coalition members’ obligations to investigate. Recognising that an obligation to investigate applies to multiple—possibly even all—States within a military coalition mitigates the diffusion of responsibility between States and can prevent investigatory efforts becoming siloed.

Conclusion: More Cooperation Required

Although improvements to investigative procedures and transparency have been made over the course of Operation Inherent Resolve (see here and here), coalition members have significantly different appetites for and approaches to investigations (p. 22). Based on lessons learned from Operation Inherent Resolve and elsewhere (p. 9-10), States involved in future military coalitions should proactively seek more cooperative and uniform processes to investigate allegations of IHL violations. This might include the creation of a centralised investigative body equipped with adequate resources and sustained cooperation from coalition States, as well as clearer, synchronised, and more accessible casualty reporting processes. Not only will this approach likely improve the effectiveness of future military operations (p. 8)—a particularly important factor in the complex context of military coalitions—it will more evidently satisfy States’ legal obligations and provide accountability for victims.

Author’s note: This post’s focus on Operation Inherent Resolve is largely based on the availability of sources. The civilian harm caused by other military coalitions in the region, involving the Syrian Arab Republic and the Russian Federation, must not be overlooked.


James Patrick Sexton is a junior researcher in public international law at the T.M.C. Asser Instituut, a research centre for international and European law based in The Hague, the Netherlands.


Photo credit: U.S. Marine Corps Capt. Ryan Alvis