Related Rule
New Zealand
Practice Relating to Rule 18. Assessment of the Effects of Attacks
New Zealand’s Military Manual (1992) states:
Those who plan or decide upon an attack shall … refrain from deciding to launch any attack which may be expected to cause incidental loss of civilian life, injury to civilians, damage to civilian objects, or a combination thereof, which would be excessive in relation to the concrete and direct military advantage anticipated. 
New Zealand, Interim Law of Armed Conflict Manual, DM 112, New Zealand Defence Force, Headquarters, Directorate of Legal Services, Wellington, November 1992, § 518(1).