Related Rule
Practice Relating to Rule 37. Open Towns and Non-Defended Localities
According to Nigeria’s Manual on the Laws of War, “firing on undefended localities” is 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 Nigeria’s opinio juris that the protection of undefended areas is part of customary international law. 
Report on the Practice of Nigeria, 1997, Chapter 1.8.