Sudan’s military is accused of using chlorine bombs: here’s how they work and what the law says

Persistent allegations of chemical weapons use in the Sudanese civil war have recently been reinforced by new evidence. US news outlets The New York Times and The Washington Post reported on materials shared by an anonymous Middle Eastern intelligence agency. The September 2026 articles paint a picture of concerted efforts by officials in the Sudanese Armed Forces to develop chlorine-based military weapons to be used against the Rapid Support Forces, particularly in and around Khartoum. The city was the stage of a prolonged battle between the army and the paramilitary forces between April 2023 and March 2025. It was characterised by heavy attacks in civilian neighbourhoods. The army took control of Khartoum in January 2026. We asked Anneleen van der Meer, who specialises in chemical weapons research, to unpack the significance of these latest findings. How does chlorine work as a chemical weapon? And what happens to people who are exposed to it? Chlorine is a chemical substance with a variety of peaceful applications. For example, the purification of water to make it suitable for drinking. It is often stored as a liquefied gas, meaning liquid under pressure. In this state, it can be transferred to munitions – military and combat equipment – and used as a weapon. When the munitions are dropped, they rip open, suddenly reducing the pressure that their contents were under. This causes the liquid to quickly evaporate into gas. Contact with this gas can cause symptoms ranging from airway irritation to pulmonary oedema, a condition that causes the lungs to flood as chemical burns damage the lung tissue. Chlorine is categorised as an asphyxiating agent, as is chloropicrine – one of the substances Russia is accused of using in Ukraine – and the stronger phosgene. These substances were used in the chemical weapons first developed and used in the first world war (1914-1918). Chlorine gas munitions in particular are a crude weapon, relatively easy to develop and assemble. Chlorine gas can be delivered via controlled release out of cylinders on the ground, mounted to artillery, or dropped out of aeroplanes or drones. Based on the evidence shared by The New York Times and The Washington Post, delivery by air was the preferred method in Sudan. As a result of its accessibility and simple assembly, chlorine was also the chemical weapon of choice of the Bashar al-Assad regime during the Syrian civil war (2011-2024). It was also mostly delivered via air, dropped out of airplanes and helicopters. What tactical advantage do chlorine bombs provide over conventional weapons? Chlorine can be lethal in high concentrations and without medical intervention. But its imprecise delivery means that it rarely is so. Moreover, while chlorine itself is fairly persistent, it evaporates quickly in high temperatures. This makes the combination of chlorine gas and explosives useful for those trying to avoid detection while retaining the advantages of a gas attack: panic, exposing fleeing targets to conventional attacks and pressure on medical services. What does international law say about the use of chemical weapons? Chemical weapons, including chlorine gas, have been outlawed for nearly a century since the Geneva protocol of 1925. They are generally regarded as inhumane by the international community, causing unnecessary suffering, and they are typically used indiscriminately. Since their first use in the first world war, chemical weapons have been subject to repeated efforts to outlaw their use, development and stockpiling. This was ultimately achieved when the international community agreed on the Chemical Weapons Convention in 1993, which entered into force in 1997. It is one of the most successful pieces of international law, with 193 signatories, including Sudan, which became a member state in 1999. States found to be in breach of international conventions that ban the use of chemical weapons are often subjected to sanctions with the aim of preventing further illegal action. This is not always successful. Both Syria and Russia have been subjected to sanctions in response to – among other allegations – the use of chemical weapons. But neither state halted its use in response to the sanctions. The Chemical Weapons Convention does not prescribe a specific course of action against transgressive states. Rather it recommends that the member states take any measures allowed by relevant international law to halt further chemical weapons use. This can include diplomatic or economic measures, but also an armed intervention if the UN security council finds the situation to be a threat to international peace and security. Individuals can also be prosecuted for the development, stockpiling or use of chemical weapons as this amounts to a war crime. An additional charge of crimes against humanity can be considered. Such cases could be pursued by the International Criminal Court, but since Sudan is not a member state, the case would have to be referred by the UN security council. Often a simpler option is for states to prosecute individuals domestically. Iraq did this with Ali Hassan al-Majid, a senior official in former president Saddam Hussein’s regime and who was better known as Chemical Ali. Syria recently did it with former president al-Assad. How could these provisions affect Sudan? Allegations of chemical weapons use in Sudan were made before the current civil war. In 2016, Amnesty International reported on the use of blistering chemicals against civilians in Darfur in that same year. However, the accuracy of this report was questioned and while the matter was discussed at international forums, no independent investigation was carried out. However, in response to the allegations of chlorine gas use between 2023 and 2025, Sudan received renewed negative attention, including sanctions from the US government in 2025. These sanctions and the international attention they generated seem to have been successful in halting the expansion of Sudan’s chemical weapons programme. The evidence shared by The New York Times suggests that Sudanese army leader Abdel al-Burhan ordered the chemical weapons programme leadership to “remove all traces” of it. The potential for prosecuting individuals in Sudan depends on the extent to which relevant international law is incorporated into Sudanese domestic law. Issues regarding this have been raised in the past. Whether or not the integration is successful will only become evident once a case is brought before a Sudanese court and a judge interprets Sudanese domestic law on this point. It remains highly concerning that states continue to turn to chemical weapons when conventional weapons fail to deliver quick results. It indicates that in the absence of critical inspection and media attention, legal prohibitions fail to restrain military commanders. This leaves civilians and combatants exposed to unacceptable risks. State signatories to the Chemical Weapons Convention should request an inspection in Sudan by the Organisation for the Prohibition of Chemical Weapons. This would signal a continued commitment to upholding the ban on chemical weapons. It would help ensure that any violation, large or small, was taken seriously.