Related Rule
Sierra Leone
Practice Relating to Rule 15. The Principle of Precautions in Attack
Section B. Avoidance or minimization of incidental damage
Sierra Leone’s Instructor Manual (2007) states:
[The principle of proportionality] requires an assessment of likely casualties, both military and civilian, and damage compared with the specific military advantage expected from the attack … The aim is to avoid or at the very least minimize collateral damage. 
Sierra Leone, The Law of Armed Conflict. Instructor Manual for the Republic of Sierra Leone Armed Forces (RSLAF), Armed Forces Education Centre, September 2007, p. 20.
[emphasis in original]