Rule 74. Chemical Weapons
Rule 74. The use of chemical weapons is prohibited.
Summary
State practice establishes this rule as a norm of customary international law applicable in both international and non-international armed conflicts.
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.[1]  At present, only 13 States are not party to either the Geneva Gas Protocol or the Chemical Weapons Convention.[2]  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.[3]  The prohibition is also contained in a number of other instruments.[4] 
Numerous military manuals restate the prohibition of the use of chemical weapons.[5]  This prohibition is also contained in the legislation of many States.[6]  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.[7]  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.[8]  There is also national case-law to the effect that the use of chemical weapons is prohibited under customary international law.[9] 
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.[10]  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.[11]  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.[12] 
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.[13]  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.[14]  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.[15] 
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.[16] 
In 1990 and 1991, the ICRC reminded the parties to the Gulf War that the use of chemical weapons was prohibited.[17]  The parties concerned had “no first use” reservations to the Geneva Gas Protocol, and the Chemical Weapons Convention did not yet exist.
Non-international armed conflicts
The prohibition of the use of chemical weapons contained in the Chemical Weapons Convention applies in all circumstances, including in non-international armed conflicts.[18]  In addition, the prohibition is contained in several other instruments pertaining also to non-international armed conflicts.[19] 
Several military manuals which apply or have been applied in non-international armed conflicts restate the prohibition on using chemical weapons.[20]  This prohibition is also contained in the legislation of numerous States.[21]  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.[22] 
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.[23]  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.[24]  The United Kingdom, for example, stated that this use was a violation of the Geneva Gas Protocol and international humanitarian law.[25] 
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”.[26] 
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.[27] 
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.[28] 

[1] Hague Declaration concerning Asphyxiating Gases (cited in Vol. II, Ch. 24, § 1); Geneva Gas Protocol (ibid., § 4); Chemical Weapons Convention, Article I (ibid., § 13); ICC Statute, Article 8(2)(b)(xviii) (ibid., § 15).
[2] Bahamas, Chad, Comoros, Democratic Republic of the Congo, Congo, Djibouti, Haiti, Honduras, Marshall Islands, Myanmar, Niue, Somalia and Vanuatu.
[3] See the statements of the Democratic Republic of the Congo (ibid., § 187), Haiti (ibid., § 240) and Honduras (ibid., § 242).
[4] See, e.g., Oxford Manual of Naval War, Article 16(1) (ibid., § 16); Report of the Commission on Responsibility (ibid., § 17); Mendoza Declaration on Chemical and Biological Weapons (ibid., § 20); Cartagena Declaration on Weapons of Mass Destruction (ibid., § 21); India-Pakistan Declaration on Prohibition of Chemical Weapons (ibid., § 22); UN Secretary-General’s Bulletin, Section 6.2 (ibid., § 24); UNTAET Regulation No. 2000/15, Section 6(1)(b)(xviii) (ibid., § 25).
[5] See, e.g., the military manuals of Australia (ibid., §§ 26–27), Belgium (ibid., § 28), Bosnia and Herzegovina (ibid., § 29), Cameroon (ibid., § 30), Canada (ibid., §§ 31–32), Colombia (ibid., § 33), Ecuador (ibid., § 34), France (ibid., §§ 35–37), Germany (ibid., §§ 38–40), Israel (ibid., § 41), Italy (ibid., § 42), Kenya (ibid., § 43), Netherlands (ibid., §§ 44–45), New Zealand (ibid., § 46), Nigeria (ibid., § 47), Russian Federation (ibid., § 48), South Africa (ibid., § 49), Spain (ibid., § 50), Switzerland (ibid., §§ 51–52), United Kingdom (ibid., §§ 53–54), United States (ibid., §§ 55–59) and Yugoslavia (ibid., § 60).
[6] See, e.g., the legislation (ibid., §§ 61–117).
[7] See, e.g., the military manuals of Israel (ibid., § 41), Netherlands (ibid., § 44), New Zealand (ibid., § 46) and United States (ibid., § 59) (prohibition of first use), the statements of Belarus (ibid., § 144), Belgium (ibid., § 150), Bulgaria (ibid., § 160), Czechoslovakia (ibid., § 196), Hungary (ibid., § 243), Italy (ibid., § 266), Democratic Kampuchea (ibid., § 279), Lesotho (ibid., § 295), Netherlands (ibid., § 320), New Zealand (ibid., § 324), Poland (ibid., § 343), Romania (ibid., § 347), Saudi Arabia (ibid., § 353), Sweden (ibid., § 371), Switzerland (ibid., § 375), Tanzania (ibid., § 379), Ukraine (ibid., § 389), USSR (ibid., § 395), United Kingdom (ibid., § 414) and United States (ibid., § 420) (prohibition of first use) and the reported practice of the Islamic Republic of Iran (ibid., § 255), Republic of Korea (ibid., § 288), South Africa (ibid., § 361) and Zimbabwe (ibid., § 443).
[8] See, e.g., the statements of Belgium (ibid., §§ 151–152), Canada (ibid., § 173), China (ibid., § 177), Denmark (ibid., § 203), Egypt (ibid., § 208), France (ibid., § 222), Germany (ibid., §§ 230 and 233), Hungary (ibid., § 243), Islamic Republic of Iran (ibid., § 250), Israel (ibid., § 260), Cambodia (and formerly Kampuchea) (ibid., §§ 278–279), Luxembourg (ibid., § 301), Mongolia (ibid., § 313), Netherlands (ibid., § 319), Norway (ibid., § 328), Peru (ibid., § 338), Portugal (ibid., § 344), Russian Federation (ibid., § 350), Sweden (ibid., §§ 371–372), Syrian Arab Republic (ibid., § 378), Turkey (ibid., § 388), USSR (ibid., § 397), United Kingdom (ibid., §§ 406–407 and 409–412), United States (ibid., §§ 397, 416, 418, 424 and 430) and Viet Nam (ibid., § 434) and the reported practice of China (ibid., § 269), India (ibid., § 332), Islamic Republic of Iran (ibid., § 255), Italy (ibid., § 264), Japan (ibid., § 269), Pakistan (ibid., § 333), Sudan (ibid., § 366) and Yugoslavia (ibid., §§ 439–440).
[9] See, e.g., Colombia, Constitutional Court, Constitutional Case No. C-225/95 (ibid., § 119); Japan, District Court of Tokyo, Shimoda case (ibid., § 120).
[10] Algeria, Angola, Bahrain, Bangladesh, China, Fiji, India, Iraq, Israel, Jordan, Democratic People’s Republic of Korea, Kuwait, Libyan Arab Jamahiriya, Nigeria, Pakistan, Papua New Guinea, Portugal, Solomon Islands, United States, Viet Nam and Yugoslavia.
[11] See the statements of Israel (ibid., §§ 260–263), Democratic People’s Republic of Korea (ibid., §§ 283–284) and Libyan Arab Jamahiriya (ibid., §§ 297–299).
[12] ICC Statute, Article 8(2)(b)(xviii) (ibid., § 15).
[13] United States, Naval Handbook (ibid., § 59).
[14] United Kingdom, Letter to the President of the UN Security Council (ibid., § 410) and Statement by the Minister of State, Foreign and Commonwealth Office (ibid., § 411); United States, Department of State, Diplomatic Note to Iraq (ibid., § 424).
[15] Iran, Islamic Republic of, Statement before the First Committee of the UN General Assembly (ibid., § 250).
[16] UN Security Council, Res. 582 (ibid., § 448), Res. 598 (ibid., § 449), Res. 612 (ibid., § 450) and Res. 620 (ibid., § 451).
[17] ICRC, Memorandum on the Applicability of International Humanitarian Law (ibid., § 505) and Press Release No. 1658 (ibid., § 506).
[18] Chemical Weapons Convention, Article I (ibid., § 13).
[19] See, e.g., Mendoza Declaration on Chemical and Biological Weapons (ibid., § 20); Cartagena Declaration on Weapons of Mass Destruction (ibid., § 21); Comprehensive Agreement on Respect for Human Rights and IHL in the Philippines, Part IV, Article 4(4) (ibid., § 23); UN Secretary-General’s Bulletin, Section 6.2 (ibid., § 24).
[20] See, e.g., the military manuals of Australia (ibid., § 26), Bosnia and Herzegovina (ibid., § 29), Canada (ibid., § 32), Colombia (ibid., § 33), Ecuador (ibid., § 34), Germany (ibid., §§ 38–40), Italy (ibid., § 42), Kenya (ibid., § 43), South Africa (ibid., § 49), Spain (ibid., § 50) and Yugoslavia (ibid., § 60).
[21] See, e.g., the legislation of Armenia (ibid., § 61), Australia (ibid., § 63), Belarus (ibid., § 65), Canada (ibid., § 68), Croatia (ibid., § 74), Czech Republic (ibid., § 75), Ecuador (ibid., § 77), Estonia (ibid., § 78), Finland (ibid., § 79), France (ibid., § 80), Georgia (ibid., § 81), Germany (ibid., § 82), India (ibid., § 84), Ireland (ibid., § 85), Italy (ibid., § 87), Japan (ibid., §§ 88–89), Kazakhstan (ibid., § 90), Republic of Korea (ibid., § 91), Luxembourg (ibid., § 92), Netherlands (ibid., § 96), New Zealand (ibid., § 97), Norway (ibid., § 98), Panama (ibid., § 99), Peru (ibid., § 100), Poland (ibid., § 102), Romania (ibid., § 103), Russian Federation (ibid., § 104), Singapore (ibid., § 105), Slovenia (ibid., § 106), South Africa (ibid., § 107), Sweden (ibid., § 108), Switzerland (ibid., §§ 109-110), Tajikistan (ibid., § 111), Ukraine (ibid., § 113), United Kingdom (ibid., § 114), United States (ibid., § 116), Yugoslavia (ibid., § 117) and Zimbabwe (ibid., § 118); see also the legislation of Bulgaria (ibid., § 66), Hungary (ibid., § 83) and Italy (ibid., § 86), the application of which is not excluded in time of non-international armed conflict.
[22] Colombia, Constitutional Court, Constitutional Case No. C-225/95 (ibid., § 119).
[23] See the statements of the Russian Federation (ibid., § 350), Sudan (ibid., § 366) and Turkey (ibid., § 388).
[24] ICTY, Tadić case, Interlocutory Appeal (ibid., § 499).
[25] United Kingdom, Statement by the FCO Spokesperson at a Press Conference (ibid., § 406) and Draft resolution submitted at the UN Commission on Human Rights (ibid., § 407).
[26] ICTY, Tadić case, Interlocutory Appeal (ibid., § 499).
[27] ICRC, Memorandum on Respect for International Humanitarian Law in Angola (ibid., § 512).
[28] See, e.g., the statements of Afghanistan (ibid., §§ 121–122), Albania (ibid., § 124), Algeria (ibid., §§ 125–126), Armenia (ibid., § 132), Australia (ibid., § 136), Austria (ibid., §§ 139–140), Bahrain (ibid., § 141), Bangladesh (ibid., § 143), Belarus (ibid., §§ 146–147), Belgium (ibid., § 153), Benin (ibid., § 154), Brazil (ibid., § 158), Bulgaria (ibid., § 162), Burkina Faso (ibid., § 166), Burma (ibid., § 167), Cameroon (ibid., § 169), Canada (ibid., §§ 172 and 174), Chile (ibid., § 176), China (ibid., §§ 178–181 and 183), Colombia (ibid., § 184), Cuba (ibid., §§ 190–191 and 194), Czech Republic (ibid., § 200), Ecuador (ibid., §§ 206–207), El Salvador (ibid., § 212), Ethiopia (ibid., §§ 213–215), Finland (ibid., § 218), France (ibid., §§ 221–222 and 224), Federal Republic of Germany (ibid., §§ 228–229), German Democratic Republic (ibid., § 231), Germany (ibid., § 233), Ghana (ibid., § 234), Greece (ibid., § 238), Guinea (ibid., § 239), Haiti (ibid., §§ 240–241), Honduras (ibid., § 242), India (ibid., §§ 244 and 246), Islamic Republic of Iran (ibid., § 253), Israel (ibid., §§ 261–263), Italy (ibid., § 268), Japan (ibid., §§ 271–272 and 275), Democratic Kampuchea (ibid., § 279), Republic of Korea (ibid., § 286), Libyan Arab Jamahiriya (ibid., §§ 298–299), Liechtenstein (ibid., § 300), Malaysia (ibid., §§ 303 and 305), Mexico (ibid., §§ 311–312), Mongolia (ibid., § 314), Nepal (ibid., § 316), Netherlands (ibid., §§ 317 and 320), Nigeria (ibid., § 327), Norway (ibid., § 329), Pakistan (ibid., § 332), Peru (ibid., § 335), Qatar (ibid., § 346), Romania (ibid., § 349), Saudi Arabia (ibid., §§ 354 and 356), South Africa (ibid., § 360), Sri Lanka (ibid., §§ 362–363), Sweden (ibid., §§ 367–369 and 371), Switzerland (ibid., § 376), Syrian Arab Republic (ibid., § 377), Thailand (ibid., §§ 381 and 383), Tunisia (ibid., § 385), Turkey (ibid., § 386), Ukraine (ibid., §§ 390–391 and 393), USSR (ibid., § 398), United Kingdom (ibid., §§ 403, 405–406 and 412), United States (ibid., §§ 427–428), Venezuela (ibid., § 433), Viet Nam (ibid., § 435), Yemen (ibid., § 437), Yugoslavia (ibid., § 438) and Zaire (ibid., § 441); see also the practice of Belarus (ibid., § 149), Belgium (ibid., § 153), Indonesia (ibid., § 248), Democratic People’s Republic of Korea (ibid., § 283) and the reported practice of Jordan (ibid., § 277).