South Africa
Practice Relating to the Use of Prohibited Weapons
South Africa’s LOAC Manual (1996) provides that “making use of … forbidden arms or ammunition” is a grave breach of the law of war and a war crime. 
South Africa, Presentation on the South African Approach to International Humanitarian Law, Appendix A, Chapter 4: International Humanitarian Law (The Law of Armed Conflict), National Defence Force, 1996, §§ 39(a) and 41.
South Africa’s Revised Civic Education Manual (2004) provides that “making use of … forbidden arms or ammunition” is a grave breach of the law of armed conflict and a war crime. 
South Africa, Revised Civic Education Manual, South African National Defence Force, 2004, Chapter 4, §§ 61(a) and 57.