Règle correspondante
Practice Relating to Rule 158. Prosecution of War Crimes
Nigeria’s Military Manual (1994) recalls:
The High Contracting Parties [to the 1977 Additional Protocol I] and the parties to the conflict shall repress breaches, and take measures necessary to suppress all other breaches of the [1949 Geneva] conventions or of [the 1977 Additional Protocol I] which result from a failure to act when under a duty to do so. 
Nigeria, International Humanitarian Law (IHL), Directorate of Legal Services, Nigerian Army, 1994, p. 9, § 9e.
Nigeria’s Manual on the Laws of War states: “The Geneva Conventions stipulate that a contracting party shall enact all necessary legislation to prohibit acts which contravene their provisions.” 
Nigeria, The Laws of War, by Lt. Col. L. Ode PSC, Nigerian Army, Lagos, undated, § 7.
Nigeria’s Geneva Conventions Act (1960) provides:
(1) If, whether in or outside the Federal Republic of Nigeria, any person, whatever his nationality, commits, or aids, abets or procures any other person to commit any such grave breach of any of the [1949 Geneva Conventions] … he shall, on conviction thereof [be punished].
(2) A person may be proceeded against, tried and sentenced in the Federal Capital for an offence under this section committed outside Nigeria as if the offence had been committed in the Federal Capital, and the offence shall, for all purposes incidental to or consequential on the trial or punishment thereof, be deemed to have been committed in the Federal Capital. 
Nigeria, Geneva Conventions Act, 1960, Section 3(1) and (2).