Related Rule
Practice Relating to Rule 6. Civilians’ Loss of Protection from Attack
Nigeria’s Operational Code of Conduct (1967) states: “Youths and school children must not be attacked unless they are engaged in open hostilities against Federal Government Forces.” It further states: “male civilians who are hostile to the Federal Forces are to be dealt with firmly but fairly”. 
Nigeria, Operational Code of Conduct for Nigerian Armed Forces, Federal Military Government of Nigeria, July 1967, § 4(b) and (j).
According to Nigeria’s Manual on the Laws of War, “participation in hostilities by civilians” is an example of a war crime. 
Nigeria, The Laws of War, by Lt. Col. L. Ode PSC, Nigerian Army, Lagos, undated, § 6.
The Report on the Practice of Nigeria states that it is the opinio juris of Nigeria that the rule that civilians are deprived of protection when they engage in hostilities against federal forces is part of customary international law. 
Report on the Practice of Nigeria, 1997, Chapter 1.2.
The Report on the Practice of Nigeria states that a presumption of civilian character is held in case of doubt. It adds that during the Nigerian civil war, “the Federal Forces in situations of such doubt did not off-handedly indict or take away individuals of such doubtful civilian character”. They subjected such individuals to a test, in order to determine
the degree of hardness of … their fingers used in handling the trigger. Those found with hardened fingers were presumed to be soldiers (combatants). Although this is an unscientific method of identification, it nonetheless shows that Nigerian practice does not prima facie attribute the status of combatant to individuals of doubtful civilian character. 
Report on the Practice of Nigeria, 1997, Answers to additional questions on Chapter 1.1.