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Nigeria
Practice Relating to Rule 96. Hostage-Taking
Nigeria’s Manual on the Laws of War provides that hostage-taking is a grave breach of the Geneva Conventions and is considered a serious war crime. 
Nigeria, The Laws of War, by Lt. Col. L. Ode PSC, Nigerian Army, Lagos, undated, § 6(c).
The manual also specifies that “killing of hostages” is a war crime. 
Nigeria, The Laws of War, by Lt. Col. L. Ode PSC, Nigerian Army, Lagos, undated, § 6(17).
Nigeria’s Geneva Conventions Act (1960) punishes any person who “whether in or outside the Federation, … 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”. 
Nigeria, Geneva Conventions Act, 1960, Section 3(1).