Rule 74. The use of chemical weapons is prohibited.
State practice establishes this rule as a norm of customary international law applicable in both international and non-international armed conflicts.
The use of chemical weapons is prohibited in international armed conflicts in a series of treaties, including the Hague Declaration concerning Asphyxiating Gases, the Geneva Gas Protocol, the Chemical Weapons Convention and the Statute of the International Criminal Court.
At present, only 13 States are not party to either the Geneva Gas Protocol or the Chemical Weapons Convention.
Of these, at least three have made statements to the effect that the use of chemical weapons is unlawful, or have indicated that they do not possess or use them or that they are committed to their elimination.
The prohibition is also contained in a number of other instruments.
Numerous military manuals restate the prohibition of the use of chemical weapons.
This prohibition is also contained in the legislation of many States.
There are numerous statements and other practice by States from all parts of the world to the effect that the use of chemical weapons is prohibited under customary international law.
Most allegations of use since the 1930s either are unsubstantiated or have been denied; the few confirmed cases have been widely denounced by other States.
There is also national case-law to the effect that the use of chemical weapons is prohibited under customary international law.
There is increasing evidence that it may now be unlawful to retaliate in kind to another State’s use of chemical weapons. There are still 21 reservations to the Geneva Gas Protocol stating that if an adverse party (and in some cases that party’s ally) does not respect the Protocol, the ratifying State will no longer consider itself bound by it.
However, 16 of these States are party to the Chemical Weapons Convention, which prohibits all use and to which no reservations are allowed. This leaves only five States (Angola, Iraq, Israel, Democratic People’s Republic of Korea and Libyan Arab Jamahiriya) which, under treaty law, could avail themselves of their reserved right to retaliate in kind to the first use of chemical weapons. Of these, three (Israel, Democratic People’s Republic of Korea and Libyan Arab Jamahiriya) have asserted that they will never use chemical weapons or are strongly committed to their elimination.
It is significant that “employing asphyxiating, poisonous or other gases, and all analogous liquids, materials or devices” is listed in the Statute of the International Criminal Court as a war crime over which the Court has jurisdiction, and that the crime is not limited to first use of such weapons.
The US Naval Handbook implies that, for non-parties to the Chemical Weapons Convention, retaliation in kind is lawful, but that it must stop once the use that prompted the retaliation has terminated.
However, in January 1991, both the United States and the United Kingdom stated that they expected Iraq to abide by its obligations under the Geneva Gas Protocol and not use chemical weapons, even though Iraq had made a “no first use” reservation.
The Islamic Republic of Iran stated in 1987 that it had never retaliated against Iraq’s use of chemical weapons, although its position at the time was that the Geneva Gas Protocol only prohibited first use.
In several resolutions between 1986 and 1988, the UN Security Council condemned the use of chemical weapons in the Iran–Iraq War without any regard to whether the use was a first use or in retaliation.
In 1990 and 1991, the ICRC reminded the parties to the Gulf War that the use of chemical weapons was prohibited.
The parties concerned had “no first use” reservations to the Geneva Gas Protocol, and the Chemical Weapons Convention did not yet exist.
The prohibition of the use of chemical weapons contained in the Chemical Weapons Convention applies in all circumstances, including in non-international armed conflicts.
In addition, the prohibition is contained in several other instruments pertaining also to non-international armed conflicts.
Several military manuals which apply or have been applied in non-international armed conflicts restate the prohibition on using chemical weapons.
This prohibition is also contained in the legislation of numerous States.
Colombia’s Constitutional Court has held that the prohibition of the use of chemical weapons in non-international armed conflicts is part of customary international law.
Allegations of use of chemical weapons by the Russian Federation in Chechnya, Sudan against armed opposition groups and Turkey in south-eastern Turkey were denied by the governments concerned.
Furthermore, as the International Criminal Tribunal for the former Yugoslavia recalled in the Tadić case
in 1995, the international community condemned Iraq’s use of chemical weapons against the Kurds.
The United Kingdom, for example, stated that this use was a violation of the Geneva Gas Protocol and international humanitarian law.
In the Tadić case
referred to above, the International Criminal Tribunal for the former Yugoslavia held that “there undisputedly emerged a general consensus in the international community on the principle that the use of [chemical] weapons is also prohibited in internal armed conflicts”.
In a Memorandum on Respect for International Humanitarian Law in Angola in 1994, the ICRC reminded the parties to the conflict that the use of chemical weapons was prohibited, although Angola had not ratified the Chemical Weapons Convention.
Practice is in conformity with the rule’s applicability in both international and non-international armed conflicts, as States generally do not have a different set of military weapons for international and non-international armed conflicts.
No official contrary practice was found. No State has claimed that chemical weapons may lawfully be used in either international or non-international armed conflicts. On the contrary, there are numerous statements to the effect that chemical weapons must never be used and must be eliminated.